~/dist/index.html

удолить:

<script src="./../node_modules/react/umd/react.development.js"></script>
    <script src="./../node_modules/react-dom/umd/react-dom.development.js"></script>

~/webpack.config.js

удолить:

externals: {
    "react": "React",
    "react-dom": "ReactDOM"
  }

Вуаля, вы великолепны!