The point is that it's not Android, so you can run whatever you can make run on mainline Linux on PinePhone, with fully supported kernel always available in uptodate state, and without any Android abstractions that may or may not limit what you can do.

Even AOSP hardcodes some reliance on Google servers. It is open source, but not independent of this dominant corporation as many privacy advocates would like.

You're still relying on closed source drivers for the vast majority of devices using AOSP, that's pretty far from "fully open source".