Except that it's now giving a huge boost to websites that use a specific technology to be fast; instead of just boosting all fast websites like it used to. Sites can be fast even if they don't use AMP.
Heck, sites can be faster if they don't use AMP. Sure, most sites aren't, but it's certainly doable. AMP, aside from Google caching your site on the SRP, doesn't really do anything crazy when it comes to site performance.