Actually the main performance gains is by google search preloading everything (basically putting it in an iFrame before you click on it). Which practically means that pages load instantly.
Google could easily adjust their ranking algorithm to better reward non-AMP pages (which they've obviously already crawled) which they know are 1) below say 75 KB and 2) contain a limited number of resources to fetch. But instead of doing that, they choose to attempt to strongarm everyone into using AMP.
https://timkadlec.com/remembers/2018-03-19-how-fast-is-amp-r...