GrapheneOS for example also is fully there already
There are some caveats to that. You do have to jump through some hoops to for instance get RCS working. I think it is worth it to feel like I'm actually in control of my device, and I would even recommend it to friends and family that I'm willing to play tech support for, but I can't truthfully say I would recommend it to an arbitrary non technical person
Not really. Might have to update the keychain first or update the package mirrors of it's a very long time but it's not a huge deal