Which is still running out of mutable storage. The point isn't whether you can verify the boot, it's whether you can prevent a compromised device (compromised to the point of being able to write to its own storage) from bricking itself.

Now, as it happens Apple (everyone really, but Apple is a leader for sure) has some great protections in place to prevent that. And that's great. But if you feel you can rely on those protections there's no need to demand the ROM recovery demanded upthread.