AMP doesn't do anything you couldn't do just by shipping an optimized website. The only difference is that you're outsourcing a lot of the experience to Google, hoping that better ad sales will balance out the loss of control.
There's also a difference from the user perspective. Presumably Google will indicate AMP content in the search results page (with an icon, etc), which will let users know the page will open "instantly." If you build a great mobile site yourself, users will never know that until they actually load your page. I can definitely see myself being more likely to open a result that I know will be performant.
Given that recent reporting has shown that ads and tracking are the biggest culprits in page load times, AMP appears to be solving an ad/tracking problem more than a web page problem.
That certainly could be the case, although I'd imagine Google will tread lightly in that regard to avoid anti-trust concerns. They've already taken a policy of using load speed as a quality signal and I wouldn't be surprised if they simply stuck with metrics like that where AMP will do well without showing any sign of favoritism.
Right, I would have much wished it provided access to dropping in native Android components (even simple things, such as a ViewPager) into a webpage. Implementing a simulated ViewPager in HTML5 including swipe gestures is a horrible CSS and JavaScript mess, a waste of resources, clunky, a choppy experience on anything but the most high-end phones, and is very easy to become inconsistent if your implementation of said gestures differs slightly from someone else's.
