this. the leverage in their arms and back, coupled with their immense grip strength, is beyond anything a human fighter will have experienced. they can and will literally rip flesh and fingers and even limbs to shreds
i remember being a little kid trying to grapple with men. it felt like trying to grapple a piece of construction machinery, the leverage the grown men could generate was just completely beyond what i could generate.
in this matchup, while a human male fighter would have a body mass advantage over the chimp, the leverage in the arms and back and the immense grip strengths i'd imagine would feel something like that - like a piece of machinery that, in this case, is trying to rip the mans face, flesh and limbs to shreds. and it's going to be biting to boot
i'm not saying a large human male with grappling / bjj and other combat experience couldn't potentially kill a male chimp - particulaly if the size advantage is significant enough - but even more important than the size advantage would be the mentality of the human combatant. if it is a man that has actually killed in war or wherever, and maybe has experience with violent wild animals; and is maybe a psycopathic violent animal himself - then maybe this man would have a reasonable chance of coming out alive. but it would be a grisly affair no doubt