Re: I would have imagined...
"I've never watched Netflix on a mobile"
I do and it's pretty much the same as you describe. The "shelves" (not sure that's a good word but I can't think of a better one) are often full of fairly recent things or popular things and some of the more niche things only turn up if searched for or by accident.
"a cunning plan to make it appear that Netflix (and Prime) have more content than they actually do"
Perhaps, but given that it is an always-changing thing it's not entirely useful as a metric. unogs.com is your friend.
Oh, and I wouldn't lump Netflix into the same category as Prime when talking about UIs. Netflix is mostly usable, Prime ought to be a textbook example of how not to design such a UI.
"plot synopsis got squeezed down to a 1-liner in most cases."
I'm less bothered by that and more bothered by when the synopsis says something like "Variety says this modern classic is not to be missed". Yeah, and? What's it about!?
"I think both are trying to meet the definition of doom-scrolling"
Doom scrolling videos? You sure you're not in the Fox News app by mistake?
For me it's more like: Oh, that looks interesting. [add to watchlist] Oh, no, not for me. Nope to that too. Oh, that looks interesting. [add to watchlist] Oh, no, not for me. Oh, that looks interesting. [add to watchlist] Oh, that looks interesting. [add to watchlist] Half an hour later: Oh, I'm too bloody tired, time for bed...