I think you’re right about the “base” skill (not sure what the right term is) of the Wizard class, “Jinx”, but… based in the info in the spreadsheet linked here, one side of the Talent Tree for the Wizard class predominantly boosts defense and health, which will make Kashhrek even harder to kill.
I don’t think I have a good enough idea yet for exactly how big the impacts are of everything class related, but I suspect a Kashhrek with maxed out Talents on the defensive side of the tree, would still be a very tough tank even for other heroes boosted with their Talents. I’m looking forward to seeing some of this in action, hopefully soon!