Graphene is more about security than privacy, but in the end they are the same. Google Play Services does not have special privileges like in normal android distributions. You can still use it as normal, I keep it in its own profile, it is sandboxed. Really nice network permissions toggle that works better than Calyx' or other distros. Hardened_malloc is an entirely new memory allocator that is safer. Their patches are sometimes used upstream by Google. The list goes on and on with GOS.
According to them, apple has good security but the trade off of course is Apple ID attaching itself to everything you do. For me, Graphene isn't any more work than any other phone, so I would have no reason to change, but that may not be the case for everyone. Some apps might not work with their implementation of google services, I don't know because I avoid those apps to begin with. I think there's a website that tries to keep this info