Honestly all jarvan needs is a lower cooldown on his ultimate so he has more presence during lanphase, his knock up is super hard to land and in the words of cyanide in his jarvan guide, LITERALLY THE WORLDS MOST FAMOUS JARVAN PLAYER WHO CHOSE JARVAN AS HIS REPRESENTATION SKIN FROM WINNING WORLDS
"if you miss your knock up, you're a minion"
the buffs I would like to see on Jarvan
-Lower cooldown on his ultimate so you have more ganking presence, if you use it during lane phase you literally don't get it back till lane phase is over
-Increase the radius on his knock up so it is easier to land for it is skinny as a nidalee spear, jarvan has to burn two skills for a maybe knock up, so if you miss it you are now in a super dangerous place with no skills in ur toolkit to use. (assuming u ganked pre 6)
-A season 5 Jarvan main who gave up on season 6