That's not a fair comparison at all. That's an actual bloodsport, which the UFC is not.

A fight wasn't stopped when a gladiator couldn't defend himself. In a Roman arena, you fought to the fucking death. Maybe against an opponent 3 times your size. Maybe against a den of lions. People held and watched these events with the explicit purpose of watching other people die.

In the UFC, once you are unable to defend yourself the fight is over. In the UFC, you can submit an opponent. Sometimes that means a fight lasts 10 seconds, with not a drop of blood spilled.

That's as apples and oranges as a comparison gets.