Unfortunately encouraging better design won't do much to most of the web. You have to guide with a heavy hand.
I'd strongly disagree. If you hit them where it hurts, they'll change. I'll even argue that we haven't really tried encouraging sites to be better.
If Google ranked load-time/page-bloat much heavier in their algorithm, and started punishing bad pages, then sites would adjust.
I currently see very little action from Google in this direction.
Look at how successful the mobile-friendly push was at getting everyone from vaguely talking about responsive designs to doing it Right Now! Every user-visible benefit of AMP would happen following your comment – increase the weight for page load time/size and add a standard pre-fetch mechanism[1] which would close most of the gap for the CDN hosting.
1. i.e. the top n results will have rel=dns-prefetch tags hoisted into the search result, the top result (or visible/hover/etc.) will have the first rel=preload html/style/script tags hoisted.
What Google should be doing is encouraging the right designs, instead of pushing their own walled-garden design.