How tank DPS focus is hurting the "trinity".

[Ivellior]

The DPS difference between the tanks is less than 5% from each other.

I don't think that is quite true. If it were true you'd be seening groups with DRK/PLD, DRK/DRK or PLD/PLD on Savage. And also quite a few people are on Savage 3 (unless you meant 4).