Found a good post by accident:
https://us.forums.blizzard.com/en/wow/t/crowd-control-diminishing-returns/728550
So there are diminishing returns on stuns. It’s still not enough though with burst dmg being so high.
You asked above what did you do after you trinketed. The answer would vary by class of course, but in short… normally not enough to survive in a 2v1 focus fire with staggered stuns. You may get off 1 GCD in between, if it is an instant, forget anything castable. Of course each class has a defensive set, I keep them hot keyed, but in may cases that’s not enough to compete with the scale of burst dps. It’s not even a fight.
Now you can get into group gameplay, of a AoE shout stun, when someone else is stunned. I understand the concepts of group pvp, and played it across a lot of different games.
I’ll just leave it at the dmg is too damn high, and the stuns are too damn long, and that comes from my personal experience playing pvp since Ultima Online. It can be done better where’s not a BOOOOM HEADSHOT Call of Duty Match.