Kurapika was created to be our Seinen surrogate. I was thinking about how the most consistently gritty and realistic character designs come from the Yorkshin and Succession War arcs, in which a serious character like Kurapika is the lead and then this came to mind. Togashi created Pika in the first place for the purpose of having a vehicle to slip into a distinctly less "shonen" narrative when he was bored of writing shonen; by that I don't mean a darker one as the Chimera Ant arc which doesn’t feature Kurapika clearly has no problem going there, but tropes and a general structure that are classically characteristic of a seinen.
In every arc where Gon and Killua are the main characters, they follow the formula of learning of their adversary, training to beat them while fighting weaker enemies, and having some personally satisfying climax (even if it's not necessarily healthy for the character, like killing Pitou). Kurapika on the other hand has already done his training and formulated a plan and backup plans by the start of his arcs-- something more befitting of a villain or old master character in shonen-- has a purposefully anticlimactic ending in Yorknew, and leads a much less rigid narrative structure where anything can happen and is propelled forward by ever raising tension with mini payoffs and misdirections which are reminiscent of a thriller (this is true of most of the series but especially so in his arcs).
So why do Kurapika’s arcs feel so natural in HxH despite taking a different narrative approach? It works because Kurapika is introduced very early and is part of establishing the series’ style and therefore its roots.