Never said to give them tp/mp regen. MCH/BRD are already the lowest dps and removing the one needed thing they bring to the raid would make them obsolete, but I'm sure there's a lot of different buffs PLD could provide. Hell, give them the ability to "pierce" enemies with their sword tip, decreasing damage resistance vs piercing weapons to compliment Drg like War/Nin. MCH and BRD would really appreciate another way to get the damage increase without having having to rely on Drg alone. Though obviously, this wouldn't help the PLD himself and wouldn't be as big a bonus.
Basically, when it comes to the holy trinity, once healing and tanking are both viable, the only really way to continue to benefit the party is increased dps or more support abilities that increase dps. As I said, it's a flaw in the system that no one has really been able to address. Except maybe GW2 and they did that by throwing the entire Trinity away.
