So since a WHM/SCH/AST has low DPS then a DRK is getting carried? It's a PLD job to Tank not DPS it's not his main role to bring the DPS that is why he is a tank!

It's not a any Tank's job to ensure the DPS check are made, or if the fight is done sooner that is the job of the DPS.

Any tank that holds Aggro on the boss and upkeeps its own survivability is doing it's job right regardless of the DPS that tank is doing. If you fail at a DPS checks then it's your DPS fault not the tanks or healers. Any DPS from them is considered a bonus.