This doesn't make any sense. Why would a google trap be "the open web"? Google & Google Cache & Google Search isn't open web. It is deductive that google doesn't show you the best resources available on the web but the ones that are of their interest.
AMP is neither of those things. It’s a library and framework for creating web pages which are then hosted on the web, openly.
In practice it's a framework for hosting web pages on Google's domain. I haven't seen any amp sites outside of the google.com domain. To call google.com "the open web" is quite a stretch. I can't control anything about google.com, and I'm bound to Google's policies and practices when hosting content there. How is this open in any meaningful sense?
Google isn't the only one that operates an AMP cache (IIRC, Microsoft, Twitter, and a couple others do), but if you get to an AMP page from Google results you'll get the version from Google’s cache.
The actual authoritative source is hosted wherever the publisher chooses, and any cache just caches that.
When I think of "not the open web", I think of walled gardens like Facebook, Apple, and Amp.