@Riot: If you want Jarvan to be a competitive pick, make this change.
Enemy units inside of R: Cataclysm are grounded.
There's no need to buff him until he's just another generic ball of stats. J4 isn't played because he's either a ball of stats or a CC bot, and his CC, including ult, is too telegraphed to be reliable vs the countless get-out-of-jail-free cards you've given champions throughout the years.
Its the same problem as Aatrox, without the sustain to make it even harder to balance. Only difference is that J4 has an easy fix to his issues that's both thematic and more satisfying for anyone playing the champion.