The people who allowed him to fight. But besides that, I think if you get a solid prosthetic arm, you can still pivot effectively with two functional legs and drive power into it, and have full mobility. Without a leg you lose both power and mobility. They're everything.
I've got a cousin that was born with 1 arm fully developed and the other stopped about 1/3 down the forearm past the elbow that ended in a rounded nub. He took a lot of teasing as a little kid and got into his share of fights for a while until folks found out he could take care of himself just fine with only one arm. He was fast on his feet, had great balance and was deceptively strong for his size. Having only one good arm helped develop the muscles and strength in that arm much faster than normal. My vote, only having one leg is a bigger disadvantage.