Look at these scans and tell me that most of his fights were just Luffy punching harder and faster, GG. Beginning of the Grandline Luffy can fight equally with Zoro, whose abilities he's extremely vulnerable to. Most of Luffy's foes said the same thing "so, you are Rubber. I'll just resort to sharp weapons, etc". Luffy would have never defeated Crocodile, Enel (until he started losing composure again), and plenty of more enemies if it wasn't for the fact that Luffy's creativity, battle smartness and incredible mobility (also a plot armor against crocodile but shh) he wouldn't have never defeated them, you are telling me punching harder worked on Arlong when he tanked Luffy's combo and shrugged it off.