In the end, its about the pedal stroke, all of it
Next time you ride and come up to another rider or a group, take a look at the rider in front of you. Watch how the leg extends at the down stroke. Watch how the feet are planted onto the pedal at that bottom of the stroke. Watch how the pelvis moves (rotates) with the pedal stroke. Watch how the knees move horizontally or remains vertically during the pedal stroke (knee drift).