<shrugs> The matter is simple. EH is a core requirement for any tank. It is what makes a tank, well, a tank. Until you have enough EH, nothing else matters very much. Cooldowns are just a better way of stacking EH than stamina. The central point of EH is the minimizing of percentage health lost.
EH balancing is not optional and between that kind of homogenization and the alternative of the progression tank divide, I'd rather take the former. My perspective comes from almost exclusively raiding 10man progression, as was promised by Blizzard in Wrath. We do not have the option of switching tanks, like a 25man raid group does. We have one warrior, one paladin, and that's it.
Easy/hard is not an acceptable solution. Warriors tanking Hyjal? I've seen it. More painful on the raid? Infinitely. Especially when the "hard" part is finding more classes to spec a certain way to chain specific cooldowns. Again, not an option open to 10man raid groups.
Do I have a problem with sharing tanking duties? Not at all. I raidlead as a tank, but nearly every boss is maintanked by our paladin, and on sizeable upgrades for both of us, I don't contest him for it.
I just want to raid, not spend my time tracking down particular classes and convincing them that our already full-to-bursting roster can somehow accomodate a few more people and forcing everyone to do sitting out rotations. It's the whole reason why I came back to raidlead 10mans after burning out late TBC on trying to raidlead 25s for two months.
"I played hard to avoid mistakes, but now I can play hard to capitalize on opportunities." -Arold, on the 3.0 Protection Warrior.