The most frustrating is that AMP version of app/pages/websites are very incomplete, e.g. the AMP version of a reddit post has only 3 comments (and the "load more comments" button is buggy). Would have been much better to use Lighthouse / PageSpeed as a basis for showing optimized pages.
Ugh, Reddit. Their amp version is terrible for the exact reason you mention. I know every time I see a Reddit page on Google results that I'll make two page loads instead of one (this does make a difference on my country, where everything is slow). Then, when accessing their pages on mobile browser, there's a huge banner telling me to download their app. In this same banner there is a dark UX pattern, where the call…
Is it just me or has the mobile web taken a nosedive in recent years? Imgur won't even let you upload images from mobile anymore without their app, reddit is getting progressively more annoying, "Get the app" buttons and modals and banners are getting progressively more prominent and dark-pattern-y, and the default for all web pages now seems to be to include regardless of whether the developers actually tested that their web page works on small screens, meaning web pages which would've just fallen back to desktop emulation mode in the past just simply don't work at all.