I would argue that the equality is in the abilities built around these principles and having each tank capable of reducing a given amount of damage (give or take 5-10%) to zero in a given timeframe.

On the WAR problem, I understand that it's a difficult balancing act but I think it would be easier to achieve if mits and heals were exclusive (though not necessarilly mutually so) and then rather than healing per se, the heals WAR would get should be seen as effective mitigation. I would balance them principly internally such that while an effect of "heals for 20% of outgoing damage" might interact with party buffs the WAR itself wouldn't have the ability to make that scale out of control.

Couldn't the magic parry be 'fixed' with a flag change though? Not saying these alone would fix what I put forth but I do consider them steps toward a solution.