Since then networks & phones got faster, a lot faster, and the difference maybe isn't worth the cost anymore. Also I think the amp restrictions have greatly relaxed, making amp just as slow? But "single worst thing"? Hardly. At launch it delivered and big time, the UX experience was night & day.
SXG and WebBundle basically help map that trick out into the browser's domain, rather than some nasty restrictive JS library. It allows eliminating the whole megabyte-sized supersystem of JS nonsense that makes up the AMP library and having just plain ol' regular HTML/JS, while still netting most of the performance benefits of the old approach.
Mobile networks may have improved but the speed of light has not, and so these techniques still have a place in contemporary networking.
All the wasted rendering for all the amp links not clicked sounds like a really great way to churn through mobile battery life unnecessarily. Glad I don't use Google.
Preferching/prerendering existed long, long before AMP did. That wasn't a new AMP technology, although it does communicate that there's going to be less to preferch than other links.
If AMP is genuinely a way to enhance online user experiences, then make it opt-in, instead of the current no-way-to-opt-out.