I set up the sandboxed Google Play Services for my gf before I gave her the phone and she's never even so much as had to ask me for help with it once, I asked her directly and she said the only issue she has is she sometimes forgets she has to confirm installing apps in the Play Store (tbf even I do that) so actually I'm saying the opposite, it's very easy to use for average users once it's installed and setup - it's the initial setup that most people won't bother with.

I've actually used Graphene OS ever since it was Copperhead and the whole time it was never more complex than normal Android, but once the sandboxed Google Play Services were announced, that's the moment I knew I could set it up, give it to any normie, and they'd have a hard time telling it apart from a stock Android phone.

The only real sacrifice is no Google Pay but luckily my gf doesn't use it and her banking app still works fine (even though it refuses to load on any other third party ROM so I'm impressed!)