Don't buy the "Android is open source" whitewashing. They just do code drops of some parts as open source where it suits them, but keep large parts as closed source when profitable/convenient. And the open source parts aren't useful on their own, because the proprietary parts are essential parts of the system's value. And then of course come the services and the platform's tight coupling to them. The services are even more closed - unnecessarily.

Real open source systems have outside contributors and stakeholders, and developer communities. Android mostly just has app developers and a "hacking" scene (xda etc).

Yes there's a small band of Quixotic guys trying to make an open source fork limp along but it's comparable in size (and odds of success) to Amiga users/developers. It's an unusable tech experiment that only runs on a couple of antiquated phones and has no services, not the Android that people know.

The only openness-related reason to prefer Android over iOS is that they still let you install what apps you like on it (sideloading) and the app store policies are slightly less draconian than Apple's.