But being able to actually utilize all your control surfaces without electrical power must be a basic requirement.

They could make the trim control wheel mechanically assisted, for example (since there are cases where electronic trim control is required because because of the amount of force needed to turn the wheel)

> They could make the trim control wheel mechanically assisted

I'd imagine it already IS mechanically assisted. There is a limit to how much you can amplify a pilot's input mechanically, and I'd imagine the load on the aircraft exceeded the amount of amplification needed.

I.e. your car has power steering, so the car manually adds power to the turn based on the user's input. That doesn't mean that something in the road can't override the input of both the driver and power steering and jerk the wheel.

Why is it possible to set the trim to insane? Is there a legitimate scenario where that would be used?

Well, the plane might be at an insane angle, so then you need an insane trim setting to correct it :)

If the AoA was truly way too high then insane trim would be required to correct that. MCAS and similar systems came about in response to AF 447 where the pilots entered a high AoA situation and stalled the plane into the Atlantic.

Is it necessarily true that you have to use the stabilizer for MCAS? Would implementing a stick pusher instead fail to avoid some stalls?

It's true in the case of the 737 MAX where the pitch-up moment caused by the engines exceeds the elevator authority in a low-speed, high-thrust situation if the pitch trim is also set too high.

MCAS will evidently work with less maximum nose-down trim than the current version has, as the proposed update places a limit on it.