Affliction as a class is designed to be focused on mass rot dmg and are of most use to the team if they're in big population areas - ex. flag area of EOTS, WSG initial middle battle, etc.. Channeling drain soul leaves you open to counterspell and will cause you to not be on top of all your other dots. I only cast drain soul on a MUST KILL kill target only after I dumped all my UAs on him. Aff lock's dmg is most noticeable if the fight is a little more organized on both sides, with healers. Aff lock's dmg will eclipse even balance druids the longer the fight draws out.
In faceroll matches, affliction can't reach up to 20 stacks and my dmg is less than others, but those games don't matter anyway.
As for PUG bgs, if the plebeians cannot figure out how to cap bases and dps I could care less now. When our DKs/locks are pulling 800k dmg there's no hope for the team. In solo queueing BGs, I've noticed alliance has 1-2 *stars* while the rest are complete keyboard turning garbage. Horde are more evenly distributed mediocre, but better than garbage.