If you brick your car's firmware, at least you can keep driving without unreasonable levels of difficulty or distraction

That's impossible for a large portion of safety critical systems. Engines don't run without a controller, they literally control the fuel injection valves (and have done so for decades). Brake systems have physical failsafes for when the electronics die (I.e. basic hydraulics without the booster), but you should not be able to move a vehicle without a working brake system after it stopped.

The shitton of software running modern cars is there for good reason (at least large chunks of it), lots of which is safety, especially in the drivetrain.

It's completely different for infotainment, which I agree the vehicle should be able to function without (although the dashboard must work)