You are acting like is not possible to buy gladiators and rank1 characters from trade. I've already seen some of those ingame backpedalling or playing horribly, giving away istantly that are purchased characters.
You gave it away by stating that warlock sucks in pvp or have bad damage/burst.
Your mindset is also the typical of a pve player which think that damage is everything and pvp is some sort of dps recount to win like in pve.
You are saying that a PVE arcane mage does more damage than a PVP warlock ? Yea no **** captain obvious, the key word here is PVE, not mage.
I've played both arcane mage and destro lock in bgs, and if they are both in pvp gear not only the warlock will do more damage, it is also more tough and can take way more punishment. With succubus out it will survive and win hunters and rogues where the arcane will simply die.
As arcane you will die vs rogues, hunters, ferals, your only shield is the mana shield which basically will get you oom if focused by 2+ ppl, and you have only 1 iceblock with crazy long cd. Without that surviving is even worse. In PVE gear? good luck doing damage while sitting in graveyard every 1 minute.
Yes, it will do nice damage if it is in a winning premade, with healers behind, vs backpedaling noobs enemies. So will do a PVE warlock.
There is more than just damage and burst in pvp (which destro lock has plenty of) or we would just play fury warriors/combat rogues/fire mages everywhere.