Runtime isolation is distinct from compile/build-time isolation. You're citing the latter, but it's the former that matters. Tesla gets this right, e.g. an interrupt in the MCU does not have any effect on braking, drive-by-wire, or ADAS systems while a car is in operation.

Just to back this up: I have rebooted both my MCU and my instrument panel while driving. Critical systems are not affected.

Fair enough, but if those bits pass through the infotainment center on the way in, controlling one allows you to control the other.