Sure but even still exploits in kernel modules are also extremely rare. The vast majority of exploits are in getting userspace to do something it has permission

Sure but even still exploits in kernel modules are also extremely rare. The vast majority of exploits are in getting userspace to do something it has permission to do but in a way that it didn't want to do it. Sandboxing & permission systems help here tremendously, which Android already has a pretty robust & extensive system (not just the normal app permissions, but also a massive set of selinux policies controlling what a given system service can do). Desktop Linux is pretty far behind the curve at this point, but Android/iOS aren't (and increasingly MacOS/Windows are fixing things up) Fuchsia seems like it'd be an incremental improvement here at best, and "real world" improvements even less clear than that.