Vengeance(the tank mechanic in MOP) will be forever remembered for needing to be removed because tanks were doing way too much damage but the playstyle and defensive usage of vengeance was the best design they ever had for that role, fully in control at all times.
I mean tanking in MOP was extremely balanced in raiding content, at a point in the expansion pally/warrior/dk/monk were all meta Druid was also usable especially for HOTW stuff. It was only cms where monks truely shined ahead.