Board Thread:Questions and Answers/@comment-26005711-20151226104253/@comment-29015906-20160712174020

I agree that Hisoka hasn't shown an interest in fighting Illumi because he knows he can win. However, there's an instance in the Alluka arc when Hisoka contemplated on killing Killua so Illumi will hate him and fight him, so maybe Illumi's willingness is also an issue for Hisoka. Maybe Hisoka wants that fight but also recognises that Illumi is too mature to engage in a senseless deathmatch unless provoked (safety of Killua). And though Hisoka is someone who will go to great lengths just for a bout with his prey, maybe he just sees that killua with his potential unlocked is a better prospect than Illumi will ever be.

Later on that same arc, Hisoka scored Illumi's aura at 95 points (based on his personal assessment) which maybe off give or take... so if by points is % compared to his maybe they are potentially equal? I guess its a matter of motivation: if Illumi fights for revenge/anger he will win; but otherwise, Hisoka will win (but such a fight will never happen given Illuka's disposition).