I wouldn't bet too much on which classes will be good, we all know how much devs love to bring out nerfs. Just play whatever class has your favorite playstyle.
If you get CC'd, you're kind of [filtered] especially if you have a Berserker or Sorcerer behind you. There was one instance I remember in K-Tera, that was a 2v2 duel. An Archer and a Priest were against a Sorcerer and Berserker. The Sorcerer managed to sleep both of them, a full charged up blow from a Berserker that crit + Hellfire that crit from the Sorcerer pretty much insta killed them both. It was kind of painful to watch haha.
It could give you elemental resistance (like in aion) + physical defense or just simply a 50% damage reduction.
Additionally, I'd implement diminishing returns, like:
CC on player A: Full duration. Next CC on player A: 50% duration. Then 40%,30% and so on; or any other way you want to scale it.
Or make it dependable on the CC: Sleep player A: full duration. Then fear player A: Full duration. Then Sleep him: 50% duration.
Additionally also an increased chance to fail a CC on a target that has already been CCed.
e.g. +5%chance to fail a CC on a target per CC that hit that target before.
Have those counters reset every 3-5 minutes.
You're forgetting the fact that zerkers too have a single hit nuke, on a 3 second cooldown if memory serves me correct (it's almost a year since I played).