On paper, yes. But in reality, the less metrics you use, the easier it will be to point what setup is the best, especially since tanks have fairly low synergy with other jobs. That's why I'm suggesting to change/add some skills to include different ways of contributing to DPS.
Maybe I'm repeating myself too much, but I really like the idea of an OT PLD using Rampart or Sentinel on someone else, which would allow the MT to stay out of tank stance even for tankbusters.
Even that can be avoided in a way, by creating more synergies with different jobs. For now, NIN loves WAR because they bring the slashing debuff. You could create a synergy between PLD/DRK and some DPS (or healers). This way, unless everybody start to play the same job, you could have different equal setup. "If you have that job, it's better to bring this tank, if you have that other job, it's better to bring this healer, etc..."
Is it difficult to balance ? Yes, it is. But it's the only way you can continue adding more and more jobs without some of them being thrown out of the elite loop.