Definitely, though, despite his low screen time, I still consider Kurapika a main character. But yeah, they all are great. I LOVE Knuckle, Shoot, Palm, and Knov. The main difference I find between each's style of writing the supporting cast, and the reason I love Kishi's supporting cast more, is that with Togashi you never question for a second whether a character is main or supporting. Though his supporting characters get their time to shine, Gon, and the other mains, are ALWAYS the center.
With Kishi, on the other hand, his supporting characters don't just get time in the spotlight - they steal it. During the time that each's respective stories are being developed, characters like Rock Lee, Gaara, Neji, and Shikimaru are, for all intents and purposes, the main characters of the series. We follow their perspective. We are given a fully developed narrative with a discreet beginning, middle and end to their character development - basically making each of their stories self-inclosed plots within the greater plot of the series. During the Kakuza/Hidan arc, Shikimaru was THE protagonist of Naruto.
The one downside to this is it is very misguiding as to being able to discern WHO is a main character. When a character like Zepile or Wing disappears from HxH, you accept it, because you always knew they were merely supporting characters. When characters like Neji and Rock Lee disappear from Naruto, however, its more difficult to accept, because, basically, Kishi's style of writing the supporting characters leads you on, and tricks you into thinking they are main characters.
No, they haven't been relevant since then. But during that time in which they were relevant, we saw completely narrative arcs come out of their characters.
Kurapika had a complete arc. Leorio had one. Knuckle, Palm, Morau and Knov had ones. Hell, Squid-guy had one!
Neji and Lee didn't have complete arcs- they were clearly set up as temporary support and nothing more. Same for Shikamaru and Kiba and Choji.Hell, you are in fact saying that Kurapika is a main character when in the 32 volumes of the manga, he appears in only 9.
Guess what, biscuit is more of a main character than him, and the only reason i won't say she isn't one is because there is, so far, only two main characters: Gon and Killua.
In terms of necessity to plot pretty much anyone besides Netero, Novu, and Morel is irrelevent when looking at one at a time on the Ant arc for the Hunter side. If Gon never existed, Pitou still can't leave Komugi and Meryem still gets blown up by the Rose, and maybe everyone else gets wiped out by Pitou (or not, because Killua might actually just cut a deal with Pitou when he's healing Komugi) but the goal of the fight was always just killing Meryem and the safety of the Hunters was never a concern. Ponz getting shot by a random ant was irrelevent to the story because Kite was already on his way to search NGL. The ragtag team of Hunters trying to make a stand against Pitou that never happened is completely irrelevent to the overall story because Meryem's fate was already sealed at that point whether this fight occured or not.
The minor characters of HXH aren't relevent to the story. They are relevent to the world. Honestly the whole Ant arc could go like Naruto's current arc where you should just have Naruto, Killerbee, and maybe two other guys and say, "Leave this to us because the rest of you are totally useless anyway." The fact that Shoot discovered his courage and then inflicted practically no damage to Yupi before getting KOed has no effect whatsoever on the outcome of the Ant arc. Even the two main characters, Gon and Killua, are irrelevent to the outcome of the Ant arc as Pitou would never be able to leave Komugi even if nobody was nearby given his unconditional loyalty to Meryem.
In Dai-no-daiboken there's a part where the nearly all-knowing Vearn asks Pop why do human beings try to fight against things that cannot be changed, and Pop answered that's because it's human to struggle to live and shine regardless of what the known outcome is. Togashi's minor characters all struggle to live, even the random guys that get killed in one frame by Hisoka or Spiders. The guy who controls dogs that was part of Kurapika's mafia group had a lover and he struggled, even though he pretty much got instantly killed. The guy with the 13 balloons that got blown away in one shot by Franklin struggled to live. In Naruto, the minor characters do not struggle. They might as well chant "Obi-wan Naruto, you're my only hope." They feel empty not because they're not given development time or that they're not relevent to the story (even the main characters of HXH aren't necessarily relevent to the overall story), but because most of them might as well be a cheerleading team for Naruto.
If you just go by the amount of material devoted to sub characters, it's almost certainly Naruto wins on volume just because Togashi is lazy. I'm not even convinced Togashi's character development has some kind of higher density per screen time though Naruto should still win easily on quantity alone. In Naruto there's a dialogue between Naruto and Jiraiya where Jiraiya says idiots can't survive in the world of ninjas and Naruto says he'd rather be an idiot if that's true. Problem is, basically everyone in Naruto is a super genius. They always know to get out of the way until Naruto or someone else powerful gets there to save the day. You'd never see anyone in Naruto die completely meaninglessly let alone do anything that ends up being detrimental to their side.
Compared to this we got people who are genuine idiots in HXH, like Knuckles. Knuckles could've waited until Yupi going bankrupt when it was clear that Yupi had no intention to pursuit him. There was no ultimate lesson to be learned for this. It was a flat out bad decision that could've gotten several more guys killed. It's a boneheaded move made by a guy who is obviously supposed to be very headstrong, which is why we consider him real. Rock Lee is said to be headstrong too, but he'd never do the same kind of boneheaded move as Knuckles because he's actually a super genius and magically knows exactly who he can fight without dying and would never get into a fight that puts his team in a worse position than they started with.