Peppers:
I should have also said there is most certainly leg drive, maybe even more so because many leapers land with a hop or with a very straight leg or sliding or too much on the toe. I can tell you personally there is no loss in velocity in the step style. I would never change a pitcher who has suffered an injury, but most importantly, one who is highly successful the way she does it.
Do you happen to have some video of step-style? I'm having a hard time visualizing a strong drive in step-style without dragging.