Again, sorry to say, but you're blowing it out of proportions. The nerf wasn't nearly bad enough to make us not viable for
heroics. Heroics are said to be designed so that they could be tanked by a non-specced tank (Arms Warrior for example).
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but cutting bonuses for both in half
That's something people brought back often, and it's inaccurate. It's the feeling you get because of the numbers you see. You see SotF going from 66% armor bonus to 33% armor bonus, but it's not like it's our only source of armor. You still get the inherent armor bonus from Bear and Thick Hide if you spec into it so, yes, you lose armor, but it's not like it's cut in half. Same with HotW, you still get the Bear natural bonus and you regain 2 of those 10% back through Imp MotW, so you don't lose that much.
I still got more health than the Prot Warrior in my guild, and I'm not fully Naxx25-geared like he is and I'm gemmed fully for Agility. I haven't checked, but I'm sure I have more armor too. The problem does not lie with the other old school tanks becoming far superior to us, it's that DK's were supposed to be nerfed to balance them but they are still grossly OP'd (Same health as a Druid, more armor, great avoidance).