We had a situation developing a few months ago where people were chaining multiple stuns together to really shut down any chance of reaction, which was pretty frustrating. We've added a recourse to Pistol Whip, Kick, and Flashbang so that can't be done anymore. While Pistol Whip and Kick do prevent most passive defenses, you can still get reactive heals. I've also got in the habit of keeping my health full, and rotating certain defensive maneuvers pro-actively to prevent dying to stun, but its definitely pretty lethal.
For me, one frustrating thing about stuns is that you sometimes have a hard time realizing your stunned (at least with Pistol Whip and Kick) as there isn't an obvious indication other than me smashing my buttons harder and harder with no avail :LOL:. If those two had the same effect as Flash Bang where it put your toolbar buttons on timer for the duration instead of just being unresponsive, at least we would be aware right away!