Here's a nice little bit of data about WF clear times on the first three expansions of the game - info is in the top voted post. I think Midas was the last tier to get any significant mechanic nerfs due to difficulty, and Creator roughly set the standard for most later Savage content.

I think tanks tend to struggle more with positioning mechanics than they do with mitigation. You can see this in the later fights of the most recent tier as well. Alongside their proposed graphical updates, I wish that they could work on updating how this game handles mob movement and animation locks. I think that if mobs could auto-attack and cleave while continuously moving like they do in Warcraft, it would allow for smoother positioning and open up the doors for more elaborate tank challenges. The problem is that every mob action is executed as a 'cast' in the combat log, which results in stutter-step movement.