Sandboxed Google Play provides better security, privacy and usability. Why that is, as well as your question about Calyx vs Graphene, is answered in this Privacy Guides Blogpost.

Ok, that's fair:)

It's not the fault of GrapheneOS that there are so few phones with the necessary security. They can't reprogram your hardware.

More importantly, it doesn't change anything about Android > iOS.

Somehow, a few people here actually DON'T BELIEVE WHAT HAPPENS NEXT – 17 minutes of comprehensive analysis and well supported arguments in favor of the claim in the title.

Wearing special anti-surveillance clothing because you want to make sure cameras can't identify you is the real life equivalent to installing ten privacy browser extensions because you want to make sure websites can't track you.