1- Each atack you Parry reduce dmg 20-25%
2- More VIT - Parry - Block the tank have more DPS i can Do as healer and surely my DPS will be more than a PLD/DRK with STR accesories - Also on warrior that 20% + healing helps HoTs a lot and let me... do more DPS.
3- If ur dungeons are taking forever u should check DPSs and urself before point the tank.

Give me my tanks full VIT/PARRY with high block rate shields and good CDs rotation, thank u