Yeah, when I was a kid I liked Kuwabara but more because I thought he was hilarious. As an adult, I appreciate him a lot more from a serious perspective, and find him much more interesting/nuanced and inspiring. I think certainly as kids, we’re very drawn to surface appeal and immediate coolness. When I was very little, my idea of a good - a.k.a. cool - character was “DRAGONS!” so I went with characters like Shiryu from Saint Seiya and Hiei until my brain started to grasp character development and differentiating characters based on that.
That said …
I was pleasantly surprised when I first started paying attention to the YYH community on tumblr because of how many active Kuwabara fans there appear to be, but I think it can also be misleading - it’s all a matter of who happens to be posting fanwork, and with less popular characters it’s often the same few passionate people posting, and it’s easy to fall into a bubble where what you see is reinforced by what you’re into.
I think it should also be noted there were and are lots of older fans in Asia even when the series first started running. (I’m an older YYH fan in North America, but probably amongst the younger cohort in Asia, because my sister read the series to me when I was little.) I think character popularity levels have remained pretty consistent around the world. Hiei is usually the most popular, Kurama closely behind (sometimes they switch, but overall it’s these two). This is reflected in heavier-investment merchandise (like figures and, lol, fashion, as opposed to gashapon keychains or whatever) - Hiei is invariably announced first, and usually Kurama comes soon after, and then it’s usually a tossup as to whether other characters (especially Kuwabara) will even be made. Meanwhile, I am sure, there are vocal Yusuke fans, and an even smaller group of Kuwabara fans probably crying with joy in the corner whenever he pops up.
With regards to popularity outside of North America and with an older nostalgic audience, here’s an anecdote - in January 2015, Taiwan (which experienced the series very closely in timeframe to Japan) held a 25th anniversary Yu Yu Hakusho doujin event complete with cosplays, doujinshi, events like “Rescue Yusuke” (lmao), etc. The series is considered very old now, so it’s relatively safe to guesstimate most fans being maybe late 20s at the youngest, with majority in their 30s, early 40s, etc.
For the event, the organizers released a set of special character cards, produced based on popularity vote. The resulting cards? Kurama, Hiei, and Koenma.
Two extra cards (Yusuke and Kuwabara) were produced in smaller quantity and had to be requested on site. From what I understand, the Yusuke card was because the fanartist loved Yusuke and drew him anyways (thank heavens not only because I love Yusuke, but it would have been kind of terrible if the main character weren’t there for his own series …). Kuwabara was illustrated apparently because one of the organizers loves Kuwabara and ended up paying for him to be made and printed. Hearing these stories warmed my heart! hahaha
I think if there were a reboot, probably in general the series as a whole would be lifted in terms of fanworks, but it’d probably stay pretty proportional to what it is today, so I don’t feel like there would be any real shift in popularity (I almost typed power here lmao, like we’re talking about Raizen dying or something). Overall my prediction would be basically more floods of Hiei and Kurama. Back in the heyday, it was really really incredible how much Hiei and Kurama doujinshi was being created lmao. The effects of this tsunami are still strongly felt even today. But who knows! :3 I don’t really have any hard data for any of my opinions, just observations. And part of it maybe really is nostalgia - a lot of people do have soft spots for their first loves and whatnot, so maybe lots of older people seeing the series for the first time with nothing to fall back on would create a shift …? (I can’t really see it, but that doesn’t make me right.)
With regards to an actual reboot, I know a lot of people in the community ache for that. Personally, I’m super torn D: I touched on this in my 30 days of yu yu answers a while back - “Why do you love Yu Yu Hakusho?”
Part of me thrills at any idea of an official Yu Yu Hakusho sequel or remake, but part of me also quails at the thought - in a way, it’s untouchable in my mind already, and everyone has their own idea of what the “right” sequel or remake would be. Never having to come up with a perfect punch line, never having to have a closed answer to what if, and not having to live up to our unrealistic expectations might be the best thing.