Sadly, I reach this conclusion as well. You have to set a strict guideline for tank and non-tank survivability with neither interlapping. Then establish your tank classes, give them the needed tools to hold hate and generate enmity at the same capacity the DPS can. Then design the boss mobs around that. It is admitedly a ton of work, but the devs have been sitting on their hands when it came to this since pre-CoP.