1. Destruction Warlocks have no defenses. There is a Demonic Circle that requires setup, is stupidly visible, doesn't break anything except for movement slowing effects, and the teleport has a cooldown. Then there is Fear, which is utterly useless as a defensive mechanic and so unreliable as an offensive mechanic that the best you can hope for is a momentary spell interrupt! Warlocks wear toilet paper armor, and no mitigation or redirection talent can make up for this. We are pet dependent in PvP, so if the Felhunter is out Rogues will absolutely slaughter us 100%. If we have the Succubus out, Mages actually become our worst nightmare (Water Elemental + Mirror Images) and will intentionally target the Warlock (Nether Protection only helps when procced and doesn't help a tremendous amount when you have a 1v5 situation like this). So there is high burst, but if you're able to catch them, there is literally nothing a Warlock can do, especially while stunned.
2. When people talk stuns, they talk Rogues and the stunlock. Being stunned 100-0 or 100-20 just sucks. But stuns and Cloak of IWIN, er, Shadows are all the Rogue has for dealing with anything (this is coming from a Warlock, so everyone can shut up). I've been stunlocked, I don't like stunlock, I've announced being stunlocked in any battleground. What I do understand though is without stuns and the stun mechanics (i.e. damage caps) Rogues become little more than Warlocks without a pet wearing Brawny paper towels. Same issue as the Destruction Warlock with large burst but the stuns provide enough for the Rogue to be effective. Removing stuns or stun damage caps would involve an absolute 700% overhaul of the Rogue class.