Salute!
I can't help but think that someone in FAA or elsewhere ( maybe even Boeing itself) is concerned about the basic aero characteristic of the MAX that even required the MCAS. In short, the plane has a pitch moment versus AoA curve that is scary. i.e. the thing wants to increase AoA with less "control force" or control surface movement or...... at high AOA. Since Orville and I soloed back in North Carolina, what we expected was to pull back harder the higher the AoA. 'course, we were directly warping the wings and moving the canard with a lever. But if we let go of the stick or neutralized it, the nose of the flyer went down all by itself.
So I
dare to show a plot from a well-known plane that illustrates an undesireable pitch moment as AoA increases. The stick neutral is a one gee command. You could get this plot by slowing down using the throttle and keeping your hand off the stick when you had trimmed for one gee ( default, BTW). The all-moving stab is progessively moving to mainain the gee, not the AoA. Somewhere about 15 degrees AoA the plane pitch moment becomes neutral, and then a degree or two higher the plane wants to raise the nose all by itself. Eeeewwwww, not good. And up there around 45 degrees you enter the falling leaf profile;
I suspect that Boeing, et al are concerned that simply using the existing stab trim mechanism to compensate for an inherent problem with the pitch moment is the "fly in the ointment".
Use of a single AoA sensor and cutting off manual electric trim to stop MCAS is a whole other thread.
Gums sends..