Earlier quoted context omitted.
The real problem is that the web is now too complex to the point that it's impossible to safely implement it. And W3C keeps trying to add new features to it. At some point we have to stop and consider whether all this cruft is even necessary.
Of course all the cruft is necessary due to compatibility. (Browsers monitor usage statistics and do remove crufts when possible.)
I actually think polyfill usage is backwards: the current approach allows code targetting new features to be made compatible with old browsers, by the site providing polyfills.
I think it's much better for new browsers to be leaner, simpler and more well-thought-out than their predecessors. Such browsers can provide polyfills to allow compatibility with code targetting old features that have been dropped.
In other words, browsers should be getting smaller (e.g. a canvas, audio stream, input method and language interpreter); more and more functionality should be offloaded into interpreted libraries (parsing, text rendering, DOM, event loops, layout, Javascript, etc.)