I think this is a big candidate for differentiating 10 vs 25m damage ranges. 10H just doesnt get hit that hard in t15 to warrant needing the extra CD. Outside of HC DA, I barely use def CDs at all. Granted I overgear the content harshly, but still. The threat just isn't there in t15 10H.
Now, the big and obvious caveat is that we don't know what 10h t16 damage looks like yet. If it's 40-50% above what we're seeing in t15, then maybe I can get behind the tank cloak, since that'd be what I consider "threatening" damage ranges. But if it stays on par with what we have now, the threat just won't be there. Which then relegates us to choosing a cape that is simply a bail-out for a fuck-up, or a non-trivial AOE DPS proc.
Well...to be fair, that's pretty damn obvious. I mean, there's no proc on the 5.3 capes, only base stats....so of course we're going to take the best itemized one. That's like saying "the only reason people take haste gear in 5.3 is because haste is good!". Well....duh
At any rate, we don't know the total proc values for DPS yet, but we know that they scale with AP and are AOE. And if we know anything about AP scaling procs, we know that they tend to border on OP for tanks (case in point, LMG). Now, considering that this proc is AOE and that there are a good many fights that involve multiple targets/adds, this proc is nothing to sneeze at. Especially in 10m where 1) tank damage matters more to group success, and 2) tank damage taken is lower, ergo not as threatening.
I'm not denegrading the AD proc, since it's clearly a powerful mechanic. I'm simply saying that from the POV of a 10H tank, the tank cape's proc is not as appealing as the DPS cape's proc.
We can get into the stat difference as well, but TBH we're going to be swimming in stats, so it's not really that much of a selling point to me (esp now that the tank itemization is less shitty).