@pihip Morihei Ueshiba was a human. So was every great martial artist in history. Any perfect simulation of a human must necessarily be fallible. AIs that have beaten human opponents, like AlphaGo, win precisely because they operate in an inhuman manner that surpasses human constraints (in the case of AlphaGo, it can simply cogitate far more potential scenarios and solutions than any person possibly could in a given time). Therefore, a machine fighting like a man is far fairer than a machine fighting like itself with no imposed weaknesses.
You do have a point with a metal/polymer body being much more durable and more taxing to hit, but this is going to be less of a factor in a grappling match. As I stated before, if it is caught in a joint-lock, its human physiology is going to guarantee its defeat.