Goldenrivet, Gordon, Mansfield,
The critical parameter is the pitch trim position (units) on the FDR; above that are indications of electrical input. The top line being the pilots yoke switches command, when enabled, the lower the FCC output - MCAS. It is quite clear during the final stages of flight, that there is little or no trim change with pilot nose up input, if indeed that was an input vice noise, but for MCAS the nose down change is quite clear - dramatic.
Additional rationale is in
Ethiopian airliner down in Africa
The argument is that excessive asymmetric control forces enable the tail trim to be repositioned nose down, but oppose all nose up movement.
Add to this that the electrical signal for trim acts directly on the trim motor at the rear of the aircraft, which can become ‘electrically stalled’ (or inhibited - under discussion). Whereas manual trim wheel from the flight deck involves cables which can stretch under high loads, this together with the unusual wheel to tail trim ratio, could appear to the pilots as having some wheel movement, but it being totally ineffective due to stretching the cables and not moving the tail trim mechanism, again due to high aerodynamic load restricting the nose - up sense.
With caveats, caution, and all reservations as above; also to be applied to
Ethiopian airliner down in Africa