

It might be not this simple in case of notification providers, the notifications are somehow sent in the name of the app I guess. And don’t forget: in general, this principle is true for most of your apps that send notifications. I.e. if you are getting Signal or Facebook notifications, it uses the same principle.
Btw, google is not the only notification service for android. Check up on Unified Push, there are many alternatives to do this, and there are some apps that support these alternatives in their non-play-store builds.

I wouldn’t really categorise it as a fuckup. These are unofficial packages from the AUR. You should trust them as much as random install scripts from a no-name website or git repo.