Just imagine that for a moment. Think how ludicrous it is that a 30 year old, former professional wrestler was able to capture the UFC heavyweight title. Now imagine he had been training BJJ and kickboxing since he was in his early twenties. That would be terrifying. Brock is probably the most freakishly athletic person in all of combat sports. He's a man who weighs close to 300 pounds, yet has the speed and agility of someone a hundred pounds lighter. Would any fighters even be able to stand up to a prime Lesnar with a well rounded game? Would history be completely different?
I realize this is completely hypothetically and imaginary, but it's kind of a fun thing to think about.