Yes we agree on that of course, both of us are/were pilots IRL and that’s what we experienced in real planes. And this the behavior we are looking for with FFB devices.
That being said, this is not the standard behavior with MSFS because it does only support regular devices whom the center position is fixed. So when the trim is moved, it emulates an effect on the elevator (*) so people can let the stick return to its center position at the same time as the trim is operated. This is not realistic at all, but this is the only solution with non-FFB devices.
So there are two solutions with FFB devices that allow to remove the pressure without actually moving the stick or yoke position:
- Either the sim’s trim ratio is left untouched, and everything is handled in the hardware
- Either the sim’s trim ratio is updated to reflect the hardware one, but in this case the aforementioned “workaround” (see * above) has to be canceled.
That’s what we can do with the ELEVATOR_TRIM_LIMIT, and it works as expected precisely because it seems to be only used by the flight model engine, and not correlated to the visuals.
For me it works perfectly: when I move my hardware trim (which actually just translates the center position in order the release the pressure):
- the trim indicator in the cockpit and the trimming wheel actually move,
- but, as expected, the pitch is not affected as long as the yoke doesn’t move.
- (I didn’t check for the trim tabs movement but I care less)
Indeed it’s surprising that this parameter only affects the flight model and not the visuals, but for this use-case it’s exactly what we want, so it’s pretty nice 
PS : I only checked with the JPL C152 but I believe this is the standard behavior. I can’t find it anymore, but I remember reading somewhere that it was actually independent. Which seems logical since MSFS flight physics are not very elaborated: AFAIK it doesn’t actually simulate the airflow depending on the surfaces positions like XPlane is supposed to do. In my understanding it’s more like higher-level formulas that combine real time variables (speed, incidence etc.) with the parameters of the flight model.