I don't see whats so hard to understand honestly it has NOTHING repeat NOTHING to do with how good ANY of the tanks DPS is PLD could be numero uno beating every DRG to top DPS slot for all my point cares.

If your group isn't good enough you could have perfect rotations the best DPS your class can do.... Maybe its your group failing not your DPS, stop looking at the tank classes themselves and thinking they fail... they all work groups have won and will keep winning with all combinations... maybe they just don't work for your group. Or maybe your group just isn't good enough in the gear you have.