So I did the quest thing just now as affliction. I've seen a lot of threads about it being nearly too hard for affliction, aswell as not having seen a video for it yet as affliction, so I decided to record it.
Reason to why I don't use my demonic gateway at all, is because it seems to be bugged at the moment and doesn't actually teleport me, aswell as it not being needed as seen in the video. You really just need to try and keep your calm as best as possible, and learn the fight as you go through it. Gear definitely seems to be a requirement, however not as good gear as some people make it seem. You can see at the end of the fight I still had quite a while to get before the "enrage" (7minute DoT thing).
My equipped ilvl is 499 and I'm using the glyph of enslave demon to make the cast lower. If anyone has any other questions, feel free to ask!
Hopefully this video might help someone