But Boeing never trained pilots how to identify the problem, and told them the old procedure was the correct way of dealing with it. The old procedure told pilots to turn electric trim off, never turn it back on and return stabilizes to neutral with manual control, which turns out to be impossible.
That's not one, but two pilot training issues with Boeing's official training materials.
A related problem is that because of the no extra training requirements, Boeing explicitly designed MCAS to be near impossible to disable, because if it was disabled then the plane now had different flight characteristics, which the pilots weren't trained to handle.
And this is also the reason why MCAS only used data from one sensor. If the sensors disagreed and MCAS disabled itself, then that would require pilot training.
The whole system would have been designed differently, and more safely if it wasn't for the "no extra training" requirement.