The pre-MAX 737 has a cut-off switch that switches of the automatic trim system, without also switching of the electric trim (there's another one that switches off the electric trim). The 737 MAX also has two switches, but they both switch off the automatic trim (including MCAS) and the electric trim.

So you can't switch off MCAS without also switching off electric trim, leaving only manual trim. But in situations like the Ethiopian flight, you need inhuman strength to control the manual trim (as Mentour Pilot demonstrates in this video: https://www.youtube.com/watch?v=aoNOVlxJmow). You need electric trim to have any chance to fight MCAS, but you can't enable electric trim without also enabling MCAS. Must be horrific to be in such a situation.

The EA crew followed that memory item. It didn't work. (Had they reduced the throttle it probably would have helped, which is why the need to limit speed during runaway trim events has been added to the updated memory item now)