> The safety drivers should theoretically be operating under the assumption that the self-driving system can fail randomly at any moment.
Then the car should be equipped with a dead man's switch / vigilance devices to ensure the driver pays attention, trains have been equipped with these equipments for decades.
> Of course, humans are not wired as reliable backups to handle random split-second problems when the system, in fact, works correctly most of the time.
Indeed, but again that is a long-known issue and we've had solutions for a long time.