Vader wasn't a particularly brilliant fighter either, though, as GL has mentioned. And Luke was learning, was becoming powerful with his released emotions, AND he was the hero at the critical point of the saga, which counts for a lot.
But none of the OT combatants would have stood a chance against the PT ones (though Obi-Wan would have been fine if he had gotten back into the 'groove'😉.
Oh, and I massively prefer Dooku to Maul, of course; he was awesome.