We are currently 1/12 HM and other than a few tank deaths because they weren't paying attention in farm content, tank mitigation is not much of an issue. Our pally tank doesn't pay attention about half the time and we can 'almost' always keep him up.
Tank damage can make for a much shorter fight, which if you don't' need to worry about dying, why not do more damage. Maybe for progression on some HM bosses it might be more useful to go full tank, but otherwise why not make the fight easier by doing more damage.
I'm in the same boat as you (boss 2 HC should go down tonight) but I just haven't had access to the tier drops which is absolutely infuriating. We have only had about 6 pieces of non (protector?) hunter/sham/monk/warr tier drop since the patch... My group seems to be insanely unlucky with drops .
As for damage incoming, it's a joke tbh. On a decent amount of fights I have my healers ask if i've bugged or something because blood shield just isn't breaking for 10-20 seconds after I pick up a boss :S.
Wait till you do Heroic Horridon, they won't be asking if you're bugged in the 'good' way then.
We are currently 5/13 heroic working on the 6th/7th simultaneously and I can't think of a fight aside from Horridon thus far that having tanks gear more 'tanky' would have been beneficial. If you time things correctly survival usually isn't an issue. On the flip side of that having tanks do more DPS is always welcomed because it makes transitions easier/faster and makes the boss die quicker.
Part of the reason I didn't tank in Vanilla/TBC was because I thought tanking was a completely brain dead role. I still don't think it's that hard today but making your DPS matter adds a lot to the role I think.