GrapheneOS have hardened_malloc which is a huge advantage, I think. It makes the weird machines problem much harder. I would say be very careful, because you can still get previews of images, or old and weird media formats that could be exploitable, and android/GrapheneOS doesn't have the same sorts of policy as say Apple with the iMessage blast door. They control safari, etc.

Android's attack surface seems pretty jagged. For example there is only one webrender engine on iOS, where you can run anything you like on Android/GrapheneOS.