TL;DR
- Efforts like Graphene OS face increasing pressure from apps that refuse to run on non-standard Android.
- The custom ROM project characterizes Google’s approach to device attestation as incomplete and flawed.
- Graphene OS is prepared to take legal action if Google won’t let it pass Play Integrity checks.
A manufacturer’s Android can have special privileges for their own apps, and almost will certainly have special privileges for Google’s apps.
Graphene by default wouldn’t give special privileges to any app, so that’s at least a plus.
It’s true that it would be locked down, but you at least have a couple more controls over how locked down compared to a manufacturer’s OS.