No, Babel and Webpack is not necessary for React stack. You can still find other alternatives to build your favourite stack such as Browserify and Gulp.
However, if you want to make things easier, I do recommend you learn and use Babel and Webpack together with React because:
- You can use modules.
- You can use JSX with ES6.
- It support a lot of browsers
- You can use more advanced features (async/await) etc
With webpack
- You can use different loaders for sass, less, postcss etc
- You can use different plugins to optimise your build such as Uglify, HotModuleReplacement, Chunks etc
There are many more advantages to use webpack which you can find here