With Jarvan becoming fomt in Top Lane, it's time to consider a few things

Before I explain myself, understand that j4 top lane won't likely go full circle until next patch when Fiora is nerfed. But you can already see a trend in both pro play and solo queue in regards to pro players: top laners are starting to pick him up more and more. For his actual level of balance, I don't find him to be particularly too strong - he's likely just right. There are numerous champions who beat him in lane, though many don't scale as well as him. Still, that doesn't matter because metas change and shift and things like lane match-ups matter less and less as a pick becomes more important due to their strengths, almost as if their weaknesses aren't really considered (that's not saying they don't have weaknesses, that's simply saying their weaknesses become less apparent due to metas).

What I'm saying is simple: Jarvan isn't a balance problem in terms of numbers. It's been proven that numbers adjustments do work on him as he's shifted in and out of the meta since his time of being on top for the better half of the season 3 jungle with the likes of Elise (though she spent a good portion of s3 being an oppressively dominate top laner whereas j4 was basically a jungler the entire time). What season 3 showed us then would likely still be true to this day: when Jarvan is good, there is literally no reason to play any other diver in the game. He outclasses all of them. He has decent damage both in the form of burst and sustained damage, decent durability and some of the best hard engage tools in the game - this being both a combination of engaging and diving (which do go hand in hand).

For the sake of the games health, I think this may actually present a problem. I know divers are on the list for class reworks, and I feel like j4 presents a pretty unique challenge. I don't think he's necessarily bad for game health, much the same way old Maokai wasn't bad for game health. But specifically for his class, he is so good at it and a variety of different things, there's no reason to play them when j4 is good. Maybe this gets fixed with the update but I'd have my doubts when considering how good j4 is at this. It shouldn't take trashing J4 to make other divers good, that's not fair to j4 players and that's not good balance either.

I don't pretend to have answers here. J4 has counterplay, j4 isn't necessarily a game health problem. But there are walls (no pun intended here) he puts up around his class that make justifying picking them over him a problem. And going forward, I do believe that needs to be addressed if you want divers to feel various once many of them get updated.