Yep. It's still not enough DPS. They did it with the holy and resto druid on 2 heal, but the holy priest wants to try sitting himself to let the resto druid work with the shaman, since he feels his spells aren't fast enough.
And we're at the point where we kick the adds into the Star every time if any are up. Both tanks are well-practiced at this point and it's our favorite part of the fight. The problem is that they'll still have a sliver of health left even after being hit by the star and then Garrosh buffs them. :P
The problem is that the adds overrun us sometimes in that both tanks wind up hamstrung so sometimes we can't grab the adds before they munch one of the two healers -- healing aggro pulls the fresh set of three onto one of them, or the co-tank dies and I solo tank the adds into Phase 2 but the RL calls a wipe anyway since we're down the second tank or one of the healers. It doesn't matter that I don't die if we go into the next phase with 1 healer or one tank. The damage meters for the better night had three DPS above both tanks; the damage meters from the worse night had me in 2nd again on the attempts where we were doing the Garrosh swap and first when we didn't bother. And before you ask, that's with the tank meta and tank cloak on. We've got a collective 1.62 million DPS between the lot of us when we drop down to two healers, with the average needed to pull off a kill being 1.99 million. So we have to make up for a 300K DPS shortfall somewhere before we can reliably proceed.
ETA: Difference between the good night and the bad night was that on the good night the uptime on the Garrosh's Hellscream buff on the adds was 7.4%, versus 22.4% with on the bad night.
Thought I'd drop in my 2 cents. We were only slightly better geared than your group when we first killed him. First, as several people have already said, you almost have to 2 heal this fight, especially when it's progression, or you just won't have enough dps. Our tanks are a warrior and a bear, I'm the warrior and the add tank. Our strat is mostly like #2 from above. I pull Garrosh to start the fight, take a few hits to get my vengeance up, then right as the adds get to the middle, the bear taunts and I gather the adds using TC for one side and DR for the the other. Since I'm the only one with any vengeance at that point, I have no problem holding the first group of adds and from that point tanking all the adds supplies me with enough vengeance to keep them off of him, with some help from him in the form of not hitting the adds. From then on I gather all the adds and our bear focuses solely on garrosh, no more switching until ph2. On the second wave of adds, I drop my mocking banner, then the third wave it's TC and DR again. If an add occasionally gets by my AoE and runs for a healer, I just taunt it back in, maybe hit it with a heroic throw. I've never had to bother with vigilance-spam taunting, as rarely do any adds get away. I tank all of the adds right on top of garrosh for the cleave/splash dmg, but the bear avoids aoe'ing them so he doesn't pull any. It isn't a huge deal now if he picks up one or two of them, but it was in the beginning.
As for dps on the adds, what you want is just enough incidental aoe/cleave dmg on them that the iron star finishes them off. As we've gotten better gear they often die or are almost dead by the time the star comes, but that wasn't always the case. They absolutely must die before the next wave comes though, or tanks are going to be taking dirt naps in a hurry, as you already know first hand. I'm 564ilvl and it's still pretty easy to die tanking 9-10 of those adds if a warsong goes off unless I have major CDs running.