At the higher levels PLD should get a job trait that allows them to attack with thier shield as apart of their auto attack cycle. It would be kind of like duel wield only with a shield instead of another weapon. The damage would be more then shild bash but there would be no stun effect. Damage, acc, and tp gain would be based on the sheild type and/or shield skill. Delay would not be effected so that it would only be based on the main hand weapon delay.
This would help PLD slightly incease damage output and tp gain while not giving up its defensive capabilities.