I'm kind of excited to make a Druid tank now
Did some math....
Apparently druid tanks get a 25% increase in stamina while warrior tanks only get a 15% health increase. However in BiS Gear, a warrior tank will still have Approx 750-1000 more health than a druid tank unbuffed.
Druid tanks will passively have more CTC than a warrior
Druid tanks will passively have more armor than a warrior
Warriors will passively take 13% less physical damage, but the same amount of magical damage.
Warriors can only block attacks, which reduces the damage received by 30%; while druids can negate the entire attack but suffers from DRs and RNG w/ dodge.
Druid tanks only have ironbark(20% 1min) and (if you pick it) Cenarion Ward(Powerful HoT. 30secCD). While Warriors have Shield Wall(40% 5min) and Last Stand(30% health increase. 3min). imo that is balanced seeing the cooldown on ironbark compared to Laststand and Shield wall.
Warrior's self heals only work when they are below 35% health. However Druids can self heal every 1 minute for over 5k noncrit(Cenarion Ward will be better in 5.2). Druids also heal themselves for 4% of their healthpool every 6 seconds when they crit(basically like having second wind but for druids).
Due to ThunderClap being melee-based(but it isn't dodge/parry-able), Warriors have better AoE threat than a Druids; but equally good single-target threat.
Druid tanks can keep Savage Defense up more active than a Warrior tank can keep up Shield Block, due to the rage-regeneration advantage from abilities. But RNG and DRs start taking into effect really vigorously when you end up tanking more than 1 NPC; Warrior tanks dont have DRs with Blocking.
My Hypothesis:
Druid tanks will passively take more damage than a Warrior tank. However a Druid tank will require LESS healing than a warrior tank will.
When Savage Defense is down, pop Cenarion Ward. Gain as much rage while Cenarion ward is up, then switch to savage defense when it's over.
When Savage Defense is down and CW is on CD, pop Ironbark. Gain as much rage as possible while Ironbark is up.
When Savage Defense is down, and Ironbark is on CD, CW should be up.
During all of that, you will be self healing yourself from your Crits.
When Savage defense is down, Ironbark is on CD, and Cenarion Ward is on CD; you then pop Berserk. This will massively increase your rage regeneration. During this time, your Savage defense will be up for about the entire cooldown on Ironbark.
After using Berserk, you'll have enough rage to last 30 seconds with Savage defense alone, but you'll actually be saving that rage to rotate Cenarion Ward and Ironbark; making that rage last even longer.
At the end of the result, Druid tanks are BiS for offtanking with little-medium healing required to keep them up. but as long as warrior's thunderclaps don't get parried/dodge and puts bleed effects on their targets; warrior tanks will still have the edge of being Main Tanks due to threat advantages from thunderclap.
On fights like garr, I really doubt a Druid tank could outplay a Warrior tank. But any tank-n-spank fights/phases; you wont even need to cast a heal on a druid tank.
