GOS is an improvement in every sense. Any app, function, or service is more private & secure on GOS than it would be elsewhere, due to it's powerful exploit mitigations
Sandboxed Google Play is done quite well. It does not give Google the special, advanced permissions it has on other AOSP systems. It is a normal app, with normal permissions. This is a GOS exclusive, and one of its flagship features
Of course, total divorce from Big G is the goal for many who seek privacy. But conducting that transitional period on GOS is more than worthwhile