In all fairness, it's pretty rare to see a guy get good ground and pound from the guard in reality against someone looking purely to tie them up and avoid damage.
Technically a heavier/shorter fighter should have probably more dangerous ground and pound than a lighter/taller one to some degree from the guard too.
Half guard should be a fair bit stronger for ground and pound though (for the guy on top), you see guys get badly roughed up in that position fairly regularly.