I have the Favero Assioma pedal based power meter, and Garmin picks up some very interesting statistics from this, such as left/right balance, torque effectiveness and pedaling smoothness, left/right power phase (where it starts and ends), peak power phase, all of which can help identify what to work on, how to get a more efficient pedal stroke.
I’ve not delved into how this data is presented in the tcx or gpx, or fit files, but the data must be there. How hard would it be to capture that information?
We don’t capture right/left power only single sided power and my guess is this is calculated by Garmin based on comparing the two pedals. So both left/right can be written to tcx/fit but then I assume analysis is done to show this data. We really try to focus on what we feel is best for most of our users so this is more esoteric analysis and also semi rare people have dual pedals indoors so not something we want to add.
Dual record with your cycling device to get those metrics. On a BLE connection it is difficult to get them, with ANT+, it´s a piece of cake.