How big is the nerf? In the comparison below I'm running the exact same gear set and the exact same talent build with the exception of Primal Gore's substitution for Omen of Clarity for testing purposes (neither talent has any effect on the numbers below). I am not rocking full best-in-slot gear due to abysmal luck with drops and giving the initial drops of Noth's bracers and Loatheb's boots to our Rogue (having to compete with Rogues for tanking gear is one of the most irritating facets of our collective Wrath experience). I'm also running a fairly stam-heavy set as much of it has to be used in my Sarth 3D tanking kit. While I'm not particularly pleased about that, I'm also not a Jewelcrafter or Leatherworker, and we don't have a Death Knight tank for Sarth 3D, so...yeah.
As an additional note, the small "buffs" you're seeing on the PTR version to dodge, attack power, and crit are the result of the new 2% stat increase from Improved Mark of the Wild. So, yes, unbuffed I have an additonal 13 AP, 0.29% dodge, and 0.20% crit as a result of IMotW. If you run a spec with 5/5 Furor instead of 2/2 IMotW and 3/5 Furor, then your attack power, crit, and dodge will not change between the live realms and the PTR.
UNBUFFED LIVE BEAR
33,853 armor (68.97% physical damage reduction before Protector of the Pack)
4854 attack power
UNBUFFED PTR BEAR
27,910 armor (64.69% physical damage reduction before Protector of the Pack)
4867 attack power
To Toskk's we go. Toskk's TTL calculator has been updated to reflect the contribution of Savage Defense (but not the HotW nerf, so I'm using 2/5 HotW at 12% stamina contribution here -- the difference between the 12% and 10% contributions doesn't have a statistically significant effect on TTL for the vast majority of current Wrath bosses), so it's safe to start running Theory Bear through her paces.
Her TTL calculation now clocks in at 10.842 seconds, with a Savage Defense shield proc of 1216.75 damage. That's pretty respectable, but if the HotW change never goes live, the TTL calculation clocks in at 11.429 seconds on an average raid boss. Essentially, the difference between a pre-nerf HotW bear and a post-nerf HotW bear is a little more than half a second to live in the same gear.
The problem isn't so much that we were nerfed; Savage Defense is going to be pretty damn good, especially if we find more +crit itemization on Ulduar gear. It's that we were nerfed without the intended compensatory mechanic going live. SD doesn't quite make up for HotW's stamina reduction, but half a second either way seems to fall pretty squarely into what Blizzard's willing to work with for tank TTL % differences. What I don't understand is why the armor nerf would go live without it, and then the HP nerf piled on top of it. The cumulative effect on bears is significantly nerfed mitigation on top of a lower HP pool, with Druids unable to make up the difference on the current PTR build in the absence of additional cooldowns or improved talents.
One reasonable explanation might be Blizzard's desire to see how much damage Druids actually take from progression raid bosses on the PTR before SD is actually implemented. Then again, bears aren't a particularly attractive choice for competitive raiding guilds on the PTR with both nerfs now live, and that may negatively affect just how much data emerges from this. So far I haven't seen a PTR kill with a Druid main tank, although it's possible I've just missed it.
What honestly worries me more than anything else is that we're being nerfed at the same time that healer mana regen mechanics are being changed so dramatically, to what ultimate effect concerning the ease of tank healing I'm not sure. Our avoidance is going to stay the lowest of all four tanks no matter what, and that necessarily bleeds into the total mana consumption of our heal teams. Our armor is going to be comparable to a decently-geared Death Knight in Frost Presence without their avoidance or cooldowns: our health is going to be comparable to a Blood-specced Death Knight without their avoidance or cooldowns: our physical damage mitigation is going to be comparable to a decently-geared Warrior or Paladin without their avoidance or, in the Warrior's case, their cooldowns: and our magic damage mitigation will continue to be worse than a Death Knight or Warrior's. On top of that, there's no buff or nerf (outside of the new Glyph of Berserk) that's aimed at addressing Bears' relatively weak capacity for burst or AoE threat.
Without additional cooldowns or tweaked talents, Bears are in kind of an iffy spot entering Tier 8 as things stand right now. Healers can afford to spam you with whatever they've got on current content, but when mana management becomes an issue, I'm somewhat concerned that the tank who is still designed to gobble most of it is going to be a significantly less attractive choice on top of providing less margin for healer error with a reduced health pool.
We'll see. I'm still interested to see if the new weighting or itemization toward +crit for Savage Defense assists with the threat issue, and we're still not far enough into Ulduar content or achievements to figure out whether bears are at a disadvantage (or advantage) in relation to other tanks.