A good way to encourage use of parry would be for a successful parry (by a tank in tank stance) should make the attack that follows it cost 0 TP. This has the dual benefit of helping TP management without altering other skills, work the same for all tanks and doesn't alter the balance of the tanks. Alternately let parry grant a 0 TP attack cost on success for all DoW classes and jobs. Tanks who stack Parry have a higher parry rate and so see a greater benefit, as they should.