If you talent Soul Leech, the breath damage is completely negated by the shield, meaning you can effectively ignore it and concentrate on keeping DoT's cleared (spamming the Breath, it's a nice boost of damage to the boss and keeps his ability to damage you low). Any additional healing can be covered by the Pit Lord's heal. Even the RoF was covered by most of the shield. Add in Glyph of Siphon Life, and you're getting a steady stream of heals as well. Both mechanics were a non-issue with that talent and glyph at 498 iLevel, and from what others have said, even as low as 485 iLevel.
I started out as Aff for this fight, and just couldn't get down the felpuppies in time. The imps were great though, SB:SoC Corr was giving tons of heals and shards. I probably could have saved some shards and bursted harder, now that I think back on it. My friend couldn't do destro and blew through it as aff though, so it is very possible. Calling either of us anything other than strictly average players is a stretch. We're great with the theory, but others can hit buttons far better than we can. I honestly thought Demo would be the best with it. Extremely good AoE, and easy to blow through the puppies after popping Meta. I think your best bet is to get rid of the addons, they're not helping and Blizzard doesn't design the game with you having to get addons anyway, and play your strongest spec with a few tweaks in talents. Blizzard was nice enough to put a rather large alert that pops up in the middle of your screen for Chaos Bolts and Cataclysms. I even got a few good blood fears off on the felpuppies after they hit me, and it was good for a bit of breathing room.
One thing is certain though. If they make Cataclysm big enough and strong enough, it would be a very effective anti-melee ability
.