The basic problem is that placates aren't tremendously powerful in PvE, since NPCs shoot very slowly, and use cooldown abilities very infrequently.

In PvP however, 3 or 4 seconds is long enough to heal to full, or to vaporize an enemy, and losing those few seconds can really screw you. So every form of CC is *much* more powerful in PvP than in PvE, which means that any CC which feels 'powerful' in PvE is likely to be stupidly overpowered in PvP.