Aspect of the Iron Hawk vs. Spirit Bond
I wrote about all of the hunter talents in MoP previously, but I wanted to take a bit closer look at these tier three talents again. First of all, here's a reminder of these two (Crouching Tiger is likely to suck so I'm excluding it):
Aspect of the Iron Hawk
Your Aspect of the Hawk now also reduces all direct damage taken by 15%
While your pet is active, you and your pet will regenerate 2% of total health every 5 seconds.
So what would these look like in a real situation? Healing versus mitigation is old hat to tanks and healers at this point, but it's fairly new for hunters to be concerned about. Let's plug in some sample numbers, where c is character health and d is damage per 5 seconds on you.
c = 175000
d = 25000
c*.02 = 3500
d*.15 = 3750
We can go ahead and find the balance where mitigation is equal to healing in terms of c and d.
With 175k health, incoming damage (mitigated by AotIH) would only have to be 23.3k damage every five seconds. That's pretty close to the example. It's also pretty small and easy to be handled by healers using limited AoE healing on everyone. I don't think they would even notice if you had your own healing or mitigation here and this is basically a best case scenario for Spirit Bond. It doesn't scale at all, unlike Aspect of the Iron Hawk. If you take a big 100k hit you'd mitigate 15k or about 21.4 seconds worth of Spirit Bond. AotIH is also proactive instead of reactive.
There are a couple other caveats to consider. AotIH says it only mitigates direct damage, so on a fight like Ultraxion that is only aoe it would presumably be worthless. Spirit Bond also heals your pet, so if you encounter a fight where the pet is not getting help from healers but is still taking damage, this could be useful. We haven't actually encountered anything like that in Cataclysm though. The only fights I can think of from this expansion where pet health was even an issue are 1) Maloriak, mostly because of the blue debuff and 2) Corrupting Parasite spawns on heroic Madness. But Spirit Bond isn't even good enough to be the solution in either of those cases (Cower works great for the latter, fyi - or simply repositioning your pet!).
AotIH is likely to be better in most situations because it scales and because preventing damage is better than healing it when those numbers are close. For the cases in which Spirit Bond does more, it's going to be because you have almost no incoming damage that can be affected by AotIH. In these cases, Spirit Bond will be either not needed or a drop in the bucket. Am I missing something?
The latest build puts Spirit Bond at 3% every 2 seconds and AotIH is a flat 15% reduction. So if we keep five second blocks, c*.075=d*.15, damage needs to be half of our total health pool every 5 seconds for AotIH to be more valuable at steady rates. Again, this doesn't say anything about the importance of big spiky hits in a pool of little damage, where AotIH is much better. Looks like they're in a good place now though.