Board Thread:Questions and Answers/@comment-26005711-20160110101622/@comment-5780397-20160110234512

Objections:

As you said, Hisoka being stronger than or equal to Illumi is just an assumption, we don't really know yet.

While what you said about the Phantom Troupe is true, but Razor could easily expel them from the island just by using a card.

Dodgeball is Razor's specialty, he trained to reflect that ball; Hisoka managed using his ability, and instead of absorbing and returning the power, took the full force of the impact, and "only" got a few broken fingers.

On the other hand, you could say that a newbie to Nen like Gon could use an ability as strong as Razor's most powerful technique.

We don't know the circumstances of their meeting. Even Johness the Dissector killed countless people before being apprehended, but that does not make him strong. Ging is not even a Blacklist Hunter, so he may have fought Razor just by chance, and the fight happened a long time ago, and Ging's strength surely increased over the years. No one said Ging was the only one who could take him down. On the other hand, Illumi killed a squadron of Hunters before any of them could press a button.

It is unknown if the "Gittarackur" ability is useful for combat: actually, since it gives him a bigger build, it may have an application that makes him stronger; or by rearranging muscles and blood vessels, he may be able to heal himself in the middle of a fight.

No, "Needlemen" was said to leave a normal person crippled for life, but it was never hinted to be ineffective against strong Nen users. Illumi even said he did not want to waste it on normal people when he used it, and Hisoka was impressed by the quantity of aura the needle had.

As shown in the Hunter Exam, Illumi's needles warp the muscles and bones in the area they hit, also causing excruciating pain.

Killua is an exceptional assassin, but even after removing the needle, he keeps being afraid of Illumi. Also, Illumi trained him, so it would not be too far-fetched to assume he has Killua's skills in martial arts and strategy, both of which enable Killua to fight and win against opponents stronger than he is.

We don't know if Illumi's puppets can use their previous abilities: if so, he may have a few at the ready before a big fight. Still, this last point is just speculation.