The issue is that the MCAS systems control over the auto-trim cannot be overridden, except by cutting out ALL powered trim.

Thats without getting into a whole gaggle of other issues like it's wide authority which RESETS every time you try to interrupt it, meaning it can trim full nose down...and that it engages the anti-stall systems automatically, which provide a force feedback on the controls to make it harder to pull the nose up.

There are quite a few interesting things in the certification documents for the 737 -8, which include issues around trim authority for the pilot being insufficient, but a ELOS being granted anyway. I'm also not particularly jazzed by their use of higher power electrical systems in the fuel tanks, which was a lesson we were meant to have learned after TWA-800 exploded.