The lack of feedback from the MCAS system is probably the killer here.
How am I supposed to know that MCAS is operating, and how do I know when to hit trim cutoff switches to override it? You don't want to ever be asking "what the heck is the airplane doing now?". Watching the trim wheel to check if it's spinning nose down all the time isn't going to work.
The behavior would be similar to runaway stabilizers, though, for which B737 pilots have memory items to perform (turn off the trim). This would have solved that problem. However, several other warnings and alerts, like stick shaker, might have been going off at the same time, making the situation chaotic and problems hard to diagnose.
