I've noticed that alot of people assume that if a fight between the two (knuckle and genthru) were to occure Knuckle would be the undisputed champion. I don't immediatly disagree with this but neither do I agree. It seems to me that people take the fact that Gon beat Genthru while being pummeled by knuckle as definitive proof but nobody seems to take the fights in context. When Gon fought Genthru, he already knew his abilities and had spent the past three weeks preparing traps, plans and training specificaly to fight Genthru (genthru had none of theese advantages), when Gon fought Knuckle he fought Knuckle he was unprepared, had no knowlage of Knuckle's nen and was barely any stronger than he previously had been (other than the last fight). Despite theese differences and granted knuckle was going easy on him, Genthru still took off one of Gon's arms and cripled the other while taking only one hit the whole time up until Gon implemented a trap that had been carefuly planned out.
Personaly I would say that Genthru is a stronger nen user than Knuckle because despite Gon having three weeks of training specific to fighting him he still managed to utterly destroy him until the pitfall trap. Gon had none of theese advantages fighting Knuckle and was in better shape after the fight than he was after facing Genthru. This isnt to say either one is weak, I've just seen and hear people put knuckle above without consideration too many times.
im curious to see if i missed anything so let me know if i did