natoal As of now I'm pretty sure of this from what I've read. I do appreciate that you need to do this extra verification (if you are paranoid, not a bad thing to be though) on 1st install but one could just mention this as a caveat instead of (almost completely) dismissing the AS approach as insecure, less private and totally not recommended.
Also you do this if you distrust AS, eg. if you believe they have been compromised or are deliberately tampering the 1st installs. Given AS is quite popular (maybe not as much as GOS) I would assume this would get noticed really fast and whistle blown. There are many folks who check their first installs of an app and others who scrutinize this kinda stuff. It's also something very easily detectable (I could do it and I consider myself an idiot). So I doubt that in practice you really need to worry about this attack vector, though ofc nothing stops you from trying to be safer.
I also feel for @pxlkng a bit here since they've been really helpful and answering a lot in such discussions so they're probably jaded by now. I'll try hitting them up on chat rooms as suggested, because I don't agree (maybe due to lack of understanding on my part) with a lot of their concerns/comparisons of AS vs Play store.
Not used chat rooms before, but I assume unlike these threads where you can dip in and out according to convenience/free-time, chat rooms would demand continuous availability? Again that's me going by the chat rooms on Stackexchange/Stackoverflow, where many groups use the same room and each group is talking about potentially orthogonal topics.