I started this quest yesterday. I have full epic gear. A combination of Timeless and ToT and SoO LFR gear. Upgraded as much as possible. I can't get past the first boss, let alone think about anything past that. I'd be fine if I could kill the adds but nothing I do works. I do Fire and Brimstone followed by Immolate and Rain of Fire. It doesn't seem to phase them very much at all. I even add in the Infernal when I can. I tried at least 20 times and only got him down to 20% twice. I started with over 1000g and now I have less than 200.
while gear does help, this quest is just meant to test your skills as a lock, i'd say, i did it in 496 gear back when it came out, it was hard, i tried about 100+ times until i got the timing right.
With SoO gear i'd imagine the quest is TOO easy nowadays.