I think your thought process is right, but the unanswered questions are:
- How frequently does the trainer measure flywheel speed and what is its sensitivity to react to changes in speed?
- over what time interval will the trainer adjust flywheel resistance over?
While it would depend a bit on the exact gear ratio you are in, a single full pedal cycle is going to lead to multiple flywheel rotations on all the trainers I’ve had.
During this one pedal cycle, there would be a small increase in flywheel speed at the ends of the “peanut” and a small decrease in flywheel speed at the indent of the peanut on the force vs angle curve.
If this small change in flywheel speed both lasts long enough within a given pedal cycle to be detected by the trainer, and is large enough to be detected by the trainer, then the trainer could still increase/decrease flywheel resistance within a pedal cycle, making the graph into a circle from a peanut.
Actually I think some power pedals can display force versus rotational angle data. Someone could figure this out for sure by going into erg mode and then graphing applied force as a function of pedal angle at both a very high cadence and a very low cadence. The two cadences would serve to make sure there isn’t a threshold speed whereby due to the sensitivity/frequency of measurement of flywheel movement, the behaviour of the trainer changes.