Also, logic wise. If Big Mom could not take down Kaido or do ANYTHING to him really, but Luffy will, his offence will be better than hers, guaranteed. That's why he needs this "advanced CoA" that Roger/WB are displaying.
Granted, Luffy cannot tank attacks like Big Mom, nor manipulate weather, so I'm not saying overall he's going to be better than Big Mom. But his OFFENCE 100% will.