sailor death dream
Alkaide
He'd be a pretty terrible fighter if he never bothered to improve after a loss.
True but it seems like he just get's strong with out even training,well never seen he train
Luffy and the rest of the crew spent two years after the Marineford Arc training. Luffy was personally trained by Rayleigh to make his haki skills stronger.
Before then, Luffy is actually pretty smart when it comes to combat and he has a knack for making things up as he goes. Nearly everything is improvised or improved improvisations from earlier in the series.
Examples:
Luffy figuring out that Crocodile's weakness is water so Luffy opted to use his own blood.
Enel's weakness to rubber.
Luffy inventing Gear Second to counteract Soru.
I'm sure there's more. I just woke up. My point is that Luffy might seem stupid but he's actually pretty clever when it comes to combat.