I agree that leaving o e foot out is not serving you well. That is the worst of the 3 options. Total commitment of both feet will train you very fast...if you still see benefit to it.

I was reminded of the benefit 2 days ago...I normally ride clipped in to my dual (spd/flat) pedals, but had to take off quickly from an intersection and so for a few seconds only had one foot clipped in, with the other on the flat...I then had to bunny hop over an obstacle and my left foot came off the pedal, rammed my shin into the pedal, and I almost crashed. I bunny hop all the time with feet clipped in with no issues, so I wasn't prepared for the foot movement.