[acdha]

It’s possible to compromise a device at the firmware level - as evidenced by the recent UEFI attacks in the wild - but the better comparison would be ransomeware. That’s shut down businesses, school systems, hospitals, etc. and is completely prevented by the iOS security model. Whether or not I like the impact on flexibility, there are inarguable benefits to the users from having devices which cannot be resold, permanently compromised, etc.

[sudosysgen]

Whether or not the uefi allows you to boot custom code has no impact on whether or not permanently compromising the uefi is possible.