Well for character's like Hanzo, we do not know how much they have improved since the Hunter Exam. If I'm not mistaken, Hanzo flawlessly beat Gon in the Tournament portion of the exam. If he has created a formidable hatsu, he may have participated in events that Hisoka finds fascinating. Or y'know, Togashi may have been watching the new anime and decided to put him in there.
Kurapika has demonstrated the ability to essentially dismantle the Phantom Troupe which is pretty impressive to say the least and Leorio, though maybe intentional, landed a hit on one of the Zodiak 12.
Also that doll of Gon is sporting quite a radical beard.
I expect both Leorio, Kurapika and Hanzo to have made some significant progress; let's not forget last time Hisoka faced Leorio he simply knocked him out with a punch to the face.
Still, Hisoka wants to face with the creme de la creme of the HxH world; guys like Satotsu, Menchi or Leorio are up there? I honestly want to know, cause the rest of the "dolls" in there are all from some pretty powerfull guys; Zodiacs, Zoldicks, Phantom Troupe and Gon/Killua/Biscuit. If they are up there, it's quite interesting.
Anyways, probably looking too much into it.