I find it hard to imagine a system that is not borkable by a superuser. Maybe it’s helpful to think of immutable setups as harder to bork by accident during routine maintenance (e.g. through faulty updates) and more resilient to bad code (through containerization).
Of all the games I played on Android I think Monument Valley was the only native mobile game that I really enjoyed. I also played Stardew Valley on mobile, that worked quite well.