It depends what they are equipped with. A minotaur typically uses an axe, while a centaur uses double swords or archery. But since its a gladitorial battle, lets assume they have no weapons. The minotaur wold have a natural weapon with his horns, and powerful legs. read more
Stronger than average, yes, but I don’t have any reason to think that the Minotaur is stronger than, say, Batman in comics. Whether or not Theseus is superhuman is debatable. He took down the Crommyonian Sow, and giant pigs in Greek mythology are usually very powerful. read more