if there was no power benefit from clipless, why are the pros still using them?
and you don't pull up to create power, you pull up just to get your weight off the pedal coming up, so the leg pushing the other pedal down doesn't have to push the weight of your other leg back up. just like walking. you lift the leg you aren't currently standing on in preparation to put it in front of the other leg. the reason this is extra effective with clipless pedals is because you don't have to worry about your foot flying off the pedal when you're putting the power down.