Remember all of Amazon Lily (far as we can tell) use Haki too. The ladies are stronger then normal marines and such I'm sure, but Luffy already beat some of the explicitly strongest on the island in beating the Gorgon Sisters. For that matter pretty sure IIRC Lufffy tore through at least one of the upper level Marines supposed to have it at Marineford. Though I'm admittedly sketchy, there.