Reason why Ivern is broken

His strength has nothing to do with what he contributes to damage in combat.

Yup. His biggest issue with being too strong is actually how strong he is at counter jungling. Even if you're fortunate enough to be on a team that reacts to whats happening in your jungle and collapses, Ivern has taken half your camps. His early counter jungle is absurdly strong and delays xp and farm to the other jungler in a role where xp and farm has already been nerfed entirely too much. If jungle xp and farm were what it was at the end of season 6, Ivern's win rate would look a lot more balanced.

Essentially, balancing Ivern by making changes to him are either going to make him entirely too strong or entirely too weak. The answer is in changing the jungle so it scales evenly with solo lanes so that junglers who get counter jungled a little by ivern (it only takes a little) aren't so far behind that they don't have decent options to catch up. Currently if a jungler farms his jungle as efficiently as possible (and by that I mean I've gone into the practice too and teleported to camps as they've spawned to reduce dead time from traveling) he will be level 5 when a solo laner who hasn't left lane reaches level 7. Now consider what happens to the jungler who loses 2 camps. Or the jungler that ganks for a lane but doesn't get anything out of it. That player is dead. This is why a support jungler like Ivern is so strong as well. Support items and gameplay are tailored around being able to influence the game while still being under farmed and under leveled.

Basically when you force a role to scale roughly equally to a lane with shared xp but without the solo lane cs gold (like supports) it shouldn't be surprising that the support champions in that role thrive relative to the others. The jungle needs changes. Nerfs need to be reverted.