Rewatching that scene made me wonder whether I should watch the films again, actually. Or reread the books? It's probably been about a decade since the first and last time I read them; I think I'd have a greater appreciation of them now.

Or does being the hero make you magically good at fighting?

Unless we get any backstory on him (literally the only thing we know about his modern-day life is that he can operate a submarine), I think we're going to have to assume this. He's just not magically good at swordfighting. Maybe Hercules trained him in hand-to-hand combat, but Atlantis's Hercules seems a bit too lazy for that to be plausible.