diff --git a/build-system/babel-config/post-closure-config.js b/build-system/babel-config/post-closure-config.js
index 17444080cdca..4fcc105fd072 100644
--- a/build-system/babel-config/post-closure-config.js
+++ b/build-system/babel-config/post-closure-config.js
@@ -32,7 +32,6 @@ function getPostClosureConfig() {
     './build-system/babel-plugins/babel-plugin-const-transformer',
     './build-system/babel-plugins/babel-plugin-transform-remove-directives',
     './build-system/babel-plugins/babel-plugin-transform-stringish-literals',
-    './build-system/babel-plugins/babel-plugin-transform-block-scoping',
   ];
   return {
     compact: false,
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/index.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/index.js
deleted file mode 100644
index 3b6a89a4ec99..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/index.js
+++ /dev/null
@@ -1,121 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-// Transforms let scoped variables into var variables, including class
-// declarations.
-//
-// Let variables inside loops that are referenced inside a
-// closure are left alone.
-//
-// Re: https://github.com/evanw/esbuild/issues/478
-// Re: https://gist.github.com/jridgewell/7a6468f61eecb467b8de265f04963286
-//
-// Input:
-// ```
-// let x = 0;
-// () => {
-//   let y = 1;
-// }
-//
-// for (let i = 0; i < 1; i++) {
-//   i;
-// }
-//
-// for (let i = 0; i < 1; i++) {
-//   () => i;
-// }
-//
-// class Foo {}
-// ```
-//
-// Output:
-// ```
-// var x = 0;
-// () => {
-//   var y = 1;
-// }
-//
-// for (var i = 0; i < 1; i++) {
-//   i;
-// }
-//
-// for (let i = 0; i < 1; i++) {
-//   () => i;
-// }
-//
-// var Foo = class {}
-// ```
-module.exports = function ({template, types: t}) {
-  return {
-    name: 'block-scoping', // not required
-    visitor: {
-      ClassDeclaration(path) {
-        const {node} = path;
-        const {id} = node;
-        if (!id) {
-          return;
-        }
-
-        const {name} = id;
-        node.type = 'ClassExpression';
-        node.id = null;
-        path.replaceWith(template.statement.ast`let ${name} = ${node}`);
-      },
-
-      VariableDeclaration(path) {
-        const {node, scope} = path;
-        if (node.kind !== 'let') {
-          return;
-        }
-
-        // We're looking for the function scope that would inherit this var
-        // declaration, and whether there is a loop scope in between.
-        const parent = path.findParent((p) => {
-          return p.isFunction() || p.isProgram() || p.isLoop();
-        });
-        const bindings = Object.keys(
-          t.getBindingIdentifiers(node, false, true)
-        );
-
-        // If the let is contained in a loop scope, then there's the
-        // possibility that a reference will be closed over in a nested
-        // function. Each loop iteration will requires its own value, which
-        // means we have to use another function to emulate the behavior.
-        if (parent.isLoop()) {
-          for (const name of bindings) {
-            const references = scope.getBinding(name).referencePaths;
-            for (const ref of references) {
-              const p = ref.findParent((p) => {
-                return p === parent || p.isFunction();
-              });
-
-              if (p.isFunction()) {
-                // The let variable is closed over. In this case, just leave
-                // the let alone instead of trying to transform it.
-                return;
-              }
-            }
-          }
-        }
-
-        for (const name of bindings) {
-          scope.rename(name);
-        }
-        node.kind = 'var';
-      },
-    },
-  };
-};
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/input.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/input.js
deleted file mode 100644
index 911611306e64..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/input.js
+++ /dev/null
@@ -1,42 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-class A {
-  method1() {}
-  method2() {}
-  static staticMethod1() {}
-}
-
-{
-  new A();
-  class A {
-    method1() {}
-    method2() {}
-    static staticMethod1() {}
-  }
-  new A();
-}
-
-function hello() {
-  new A();
-  class A {
-    method1() {}
-    method2() {}
-    static staticMethod1() {}
-  }
-  new A();
-}
-
-new A();
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/options.json b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/options.json
deleted file mode 100644
index a47282a6be9a..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "plugins": ["../../../.."]
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/output.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/output.js
deleted file mode 100644
index 6f6eeb3ec6db..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-class-declaration/transform-class/output.js
+++ /dev/null
@@ -1,55 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-var _A = class {
-  method1() {}
-
-  method2() {}
-
-  static staticMethod1() {}
-
-};
-
-{
-  new _A2();
-
-  var _A2 = class {
-    method1() {}
-
-    method2() {}
-
-    static staticMethod1() {}
-
-  };
-
-  new _A2();
-}
-
-function hello() {
-  new _A3();
-
-  var _A3 = class {
-    method1() {}
-
-    method2() {}
-
-    static staticMethod1() {}
-
-  };
-
-  new _A3();
-}
-
-new _A();
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/input.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/input.js
deleted file mode 100644
index f80b4d4893e0..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/input.js
+++ /dev/null
@@ -1,38 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-const a = 'abc';
-
-{
-  const a = 'xyz';
-}
-
-function test() {
-  const a = 1;
-  {
-    const a = 2;
-    const b = 2;
-  }
-}
-
-const z = [];
-
-for (const i = 0; i < 10; i++) {
-  z.push(function() {
-    return function() {
-      console.log(i);
-    };
-  });
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/options.json b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/options.json
deleted file mode 100644
index a47282a6be9a..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "plugins": ["../../../.."]
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/output.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/output.js
deleted file mode 100644
index db44958fd3c7..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/no-transform-const/output.js
+++ /dev/null
@@ -1,37 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-const a = 'abc';
-{
-  const a = 'xyz';
-}
-
-function test() {
-  const a = 1;
-  {
-    const a = 2;
-    const b = 2;
-  }
-}
-
-const z = [];
-
-for (const i = 0; i < 10; i++) {
-  z.push(function () {
-    return function () {
-      console.log(i);
-    };
-  });
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/input.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/input.js
deleted file mode 100644
index 2a72fa28cdca..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/input.js
+++ /dev/null
@@ -1,43 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-let a = 'abc';
-{
-  let a = 'xyz';
-  console.log(a);
-}
-console.log(a);
-
-function test() {
-  let a = 1;
-  {
-    let a = 2;
-    console.log(a);
-  }
-  console.log(a);
-}
-
-let z = [];
-
-for (let i = 0; i < 10; i++) {
-  z.push(function() {
-    console.log(i);
-  });
-
-  let x = i;
-  z.push(function() {
-    console.log(x);
-  });
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/options.json b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/options.json
deleted file mode 100644
index a47282a6be9a..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "plugins": ["../../../.."]
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/output.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/output.js
deleted file mode 100644
index 9732c34fe3f0..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/fixtures/transform-variable-declaration/transform-let/output.js
+++ /dev/null
@@ -1,44 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-var _a = 'abc';
-{
-  var _a2 = 'xyz';
-  console.log(_a2);
-}
-console.log(_a);
-
-function test() {
-  var _a3 = 1;
-  {
-    var _a4 = 2;
-    console.log(_a4);
-  }
-  console.log(_a3);
-}
-
-var _z = [];
-
-for (let i = 0; i < 10; i++) {
-  _z.push(function () {
-    console.log(i);
-  });
-
-  let x = i;
-
-  _z.push(function () {
-    console.log(x);
-  });
-}
diff --git a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/index.js b/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/index.js
deleted file mode 100644
index bb2e50c56b6a..000000000000
--- a/build-system/babel-plugins/babel-plugin-transform-block-scoping/test/index.js
+++ /dev/null
@@ -1,19 +0,0 @@
-/**
- * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS-IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-const runner = require('@babel/helper-plugin-test-runner').default;
-
-runner(__dirname);
diff --git a/build-system/compile/post-closure-babel.js b/build-system/compile/post-closure-babel.js
index 1bf5cdc38731..2d068dae8eb5 100644
--- a/build-system/compile/post-closure-babel.js
+++ b/build-system/compile/post-closure-babel.js
@@ -30,7 +30,7 @@ const {debug, CompilationLifecycles} = require('./debug-compilation-lifecycle');
  */
 async function terserMinify(code) {
   const minified = await terser.minify(code, {
-    mangle: true,
+    mangle: false,
     compress: {
       defaults: false,
       unused: true,