Prior to 3.1, druids were the optimal offtank. This was because of a variety of reasons, but most notably because of two primary factors:
1. Their gear could be used for both DPS and tanking in some reasonable fashion
2. Their spec could be tailored to do both good tanking and good DPS at the same time without a respec
This meant that a feral could reasonably be expected to DPS and tank and know both roles well. This was a continuation of the BC model, and in fact actually improved on it due to how they nerfed armor in 3.0.8. Now you could not only just change gear and DPS or tank, you didn't have to change gear! You could just tank in whatever and be fine.
In 3.1, this changes a bit with the advent of dual specs. It's expected that all tanking classes will have at least one 'useful' other spec in my guild so that they can switch if necessary and not be a total gimp for an encounter while still having a chance at drops. That's the real key; if they didn't need anything from that boss, they'd simply sit out in favor of a better DPSer. I'll get to why this is in a second.
This entirely removes factor 2 from the equation above. If any warrior can spec to DPS before a fight, being able to tank and DPS in the same spec is functionally irrelevant. It might be convenient, and it might allow things like a feral's secondary spec to be resto - but it's not affecting anything in a raid, exactly.
Here's the thing though, and what I fully expect to get a lot of flak for: ferals are still going to be the best offtank. Here's the list why:
- Any fight that has a tank requirement for only part of the fight. A feral will have significant advantages over other tanks. Even in full tanking gear and a full tanking spec a feral druid does significantly more damage than any other tank. Not as much as a full cat spec and good cat gear, but we're talking about a 1k difference in DPS between a feral and a prot warrior. This is slightly not as good as it was in 3.0.8 due to the higher stamina requirements on gear/enchants/trinkets, but at the same time a lot of dps and tanking gear is shared. It helps that the T8.25 gear is superior for bears, stat wise, but also has superior set bonuses for cats too - that's another set of gear that is almost certainly going to be shared.
So fights like Thaddius or Malygos where a second tank is needed only some of the time? Druids win, hands down. That being said, there aren't that many opportunities for this sort of min-maxxing in Ulduar. Iron council could use the third tank to swap to dps. XT could use an offtank picking up adds on the phase change. And...that's about it, at least so far as we know. Not exactly stunning, right?
- Ferals will have superior DPS gear over other tanks. Now, this might not be true going into Ulduar. Guilds which have had everything on farm for months may have all of their tanks totally outfitted in offspec DPS gear to the point where they're as well-geared as the next DPSer. I don't believe this will be true (betrayer of humanity doesn't drop nearly enough for us, for example), but even if it is, it won't matter. Because as soon as a feral gets their first tier drop, they're better geared for both tanking AND dps than any other tank. Any other tank must get two sets of tier gear, a separate weapon (or weapons), trinkets and sets of jewelry, etc. A feral can continue to double dip and get close to or best in slot for many slots and gem/enchant them optimally for either role. As it stands right now a druid can (for example) get T8.25 gloves and chest and gem/enchant them optimally for both bear and cat in one go. The best DPS trinket is also the best tanking trinket (or one of them at least). Favor of the Dragon Queen is still one of the best tanking necks. This isn't as true now as it was before due to the higher requirement of gemming/enchanting/gearing for stamina that the 3.1 HotW nerf does, but a smart bear will try and maximize as many shared pieces as possible and then get two sets of gear when the gems/enchants differ significantly to offer a clear advantage (the head and legs are two traditional options, and others can be depending on profession).
Any other tank does not remotely have this flexibility. Even a death knight using DPS 2-handers as their weapon still must enchant for tanking or DPS. Because of the stamina and defense requirements for plate gear, virtually no shared gear exists for plate wearers. The long and short of it is that even if a feral's DPS gear is on par with a tank's DPS gear now, they'll quickly have an advantage when getting more gear in Ulduar. A good raid leader will maximize this advantage. Furthermore, even if the gear can't be shared most of the gear is still DPS-centric. A helm enchanted with Stalwart Protector and gemmed with Austere isn't as good as a DPS-centric helm, but it's still a leather helm with tons of agility and AP. Plate tanks have virtually nothing that can double in this way. Thus, it will take significantly longer for the plate wearers to get comparable DPS gear to the ferals - and by the time they do, chances are the encounters will be on farm.
- Ferals will tend to have more experience DPSing. This one I admit is very subjective, but I think it's realistic. The amount of people that roll ferals and know nothing about DPS is I think quite small. The ferals I've encountered have known quite a bit about both how to tank and how to DPS. BC ferals had a lot of experience DPSing as a feral while being expected to offtank here and there, if not tanking the whole way. That was the BC way: if you as a feral weren't willing to tank and DPS, you weren't really pulling your weight.
Plate tanks are not necessarily so inclined. Some will have been DPSers for a while at some point, or even prefer it. Others will have rolled that warrior to tank first and foremost, and have no interest or inclination to DPS. Others will have simply never dabbled in it at all; as an example, one of our tanks went from a prot paladin to ret for the first time on Brutallus.
I realize that this is entirely anecdotal, and there exist no hard numbers to compute that show how many ferals prefer only doing bear, only doing cat, or doing both in some fashion. I still suspect that this is so. I'm curious what others out there think.
- No other tank can tank as well in DPS gear if you really need to. This is more of the 'hero' thing that you see now and then. Because of Survival of the Fittest and how armor works, and even with the HotW nerf, ferals will still be able to switch to bear and tank adequately in some situations while wearing DPS gear. They won't have as high of stamina as another tank, but they'll have far higher stamina than a DPS of another class will. They won't take crits either, and their avoidance and threat numbers should be significantly higher. Whereas if you ask a ret paladin to tank in a pinch, they'll have significantly less armor, avoidance, and huge gulfs in stamina as well as not being able to avoid taking critical hits.
- Innervate and battle res are huge raid buffs that are impractical often when tanking 100% of the time. This speaks to the scenario where you have two or more tanks and you're trying to figure out which to have swap spec. Do you have the prot paladin go ret (so you have two ret) or do you have the feral go cat? All the other raidwide buffs can be covered by another feral or other classes entirely, but single abilities are not. Another battle res and innervate for a progression encounter can mean the difference between a wipe and a win. At the same time, there are plenty of fights where if you are tanking, you can simply not reasonably do this. Ulduar has these in spades: Ignis, Vezax, Hodir practically, Freya, Auriyaya - none of these fights have significant breaks where you could reasonably expect to res someone if you're in the middle of tanking. Other fights like XT or Iron Council have breaks where you can, but you might not be able to when you need to.
Does any other tank bring this kind of class utility? Not particularly. The closest might be a paladin, but most of that utility is in raid buffs which they would bring anyway while tanking.
Now, what this does not mean is that I am saying that ferals are only good for offtanking in Ulduar. Make sure you understand that. For the record I don't think ferals are significantly disadvantaged in fights in Ulduar as they stand and as we know about them - though I also think that other tanks bring significant advantages to tanking encounters that druids really don't. The only fight where a feral may make it easier is on normal-mode Hodir, where they can wear FR gear and still tank significantly. Pretty much everything else favors another tank, primarily because of cooldowns and avoidance. Still, there's nothing that says a feral can't tank anything in there, so if that's what your raid feels is best for whatever reason (skill, gear, experience, social reasons) that should be fine.
I personally am a bit saddened by this, as I don't like the notion that because other tanks can't do DPS that ferals are basically forced to. This was the model for BT, and it wasn't fun at all. Some solutions I've seen have been to enforce specific gearing requirements for tanking similar to how they were in BC (with armor and defense/resilience) and allowing innervate/brez in bear form with a talent (but only in bear, so cats wouldn't want it). And personally it doesn't really matter a ton; my raiding time is much constrained for the future, and I'll likely be doing it only part-time if that (and often, raiding on my wife's toon, a holy priest). Still, I'd like to see more fights advantage druids or at least level the playing field a bit, and I'd like to see other tanks get more incentive to do DPS (or possibly disincentivize druids a bit).