Hmm your gearing and technique is adapted to make use of the pulling-up capability of clipless. When going up 'high resistance terrain' I get into granny gear and spin fast - too fast for my legs to actually pull on the upstroke. Different.
I've done a lot of single pedal drills on a turbo, when one goes for a significant amount of time with only one foot on the pedal you develop a very efficient pedal stroke, where you pedal in circles rather than up & down letting the cranks guide your foot. While this doesn't mean you produce power on the upstroke normally you do quickly get to a point where for the vast majority of the upstroke our foot is effectively unweighted on the pedal. For me even at 130rpm I've only got useful downward pressure (>0.15N) on the pedal for 25-35 degrees of the upstroke leaving the remainder with 0 pressure or slight upwards force.
Your figures seem plausible, but, for aerobic climbing, conventional wisdom says the limiting factor is not your legs, but your cardio output, no?
FTP over 1h is about 210w @ 110 (+/-20) rpm, if I mix up the cadence & the pedal style I can add another 20-25w to that for 40-45 min, maybe longer I've never tried to hold on longer than that, by driving one group of muscles into mild oxygen debt while others rest & recuperate. Part of that process is using more upstroke & less downstroke essentially you have 4 options:
1) in the saddle without upstroke assistance
2) in the saddle with upstroke assistance
3) out the saddle without upstroke assistance
4) out the saddle with upstroke assistance
Within those options your choice of cadence (& position in the saddle) can change the exact utilisation of your muscles. Also it takes less power to lift the leg up than push it up with the pedal which goes back to the pedal drills.