It wouldn't really make it any more interesting. Even if he handicapped himself somehow (which he actually practically does all the time since he doesn't need to go all out), it would be meaningless as he would still know he can end the fight any time he wants (he doesn't even rely on a weapon he could leave home to weaken himself). It would be just poor taste with the opponent still fighting for their life. It's only a bit more meaningful, and thus interesting, if he's fooling around with a friendly person like Genos, as he could derive from satisfaction from seeing the opponent's progress and innovation. Kind of a like a good teacher would be happy when seeing the students thrive.