> It gives Google control over serving the content
Fair point. They're planning to fix this with the upcoming Web Package Standard though, so it won't be an issue for much longer.
> and how it's ranked when users search for it
That's just as true for non-AMP content.
> Most AMP pages look very similar to me.
AMP provides a bunch of prebuilt components developers can use to construct their pages, so I suspect what you're noticing here is developers just taking the path of least resistance. (Kinda like how sites built with Bootstrap tend to look similar.) With a little effort, AMP pages _can_ differentiate themselves. For example, these are all AMP pages:
* https://tasty.co/
* https://magebit.com/
* https://www.myntra.com/amp/lipstick