We're not really speaking about the same PVP if you're talking about locking up an entire group to death. That doesn't happen at higher ranks in CC. What does happen, however, are people dropping like flies to the holy trinity of rotated CC: Silence >> Poly >> Stun >> Death. Its a deadly combo because most people won't cleanse the silence because they don't consider it "a threat like stun", which leads to their doom: you can't cleanse the Poly and that's 4 seconds of you getting wailed on with 0 counterplay. A simple stun afterwards seals the deal, because you won't have the reactions to mash purify before the last 20% of your health gets chopped off during the beginning of the stun.
I went from not caring about silence to absolutely dreading it once I got into a high enough bracket where people make use of it. Its a subtle and non-offensive CC on the surface, because you can still move, you just can't act, so you think you're safe, but not really. I now purge silence on reaction, especially when I know a high-damaging rdm is on the enemy CC team.
If you're talking about generic frontlines matches, then yeah, Mongo barbarian AOE stun is the tits, but WHM's LB is far, far worse, and up almost just as often. War stun in CC is great, but its not what makes War so deadly: its the fact that none of the other tanks have anything like it on such a low cooldown. Drk is a god - when its LB is up. Pld is a god - once every 30 seconds. Gnb is... something, lol. That job needs some serious love.