Need? Nothing, really. Like I said, no changes are actually necessary for RA. It's just that it seems rather odd that it is literally the only Tank combo in the game that had no additional effects whatsoever.
A few people have mentioned in the past that they'd like to see it provide raid utility of some kind, like a dmg buff. Personally, I'm not too fond of this idea, because I think that it would make Pld's too similar to War's. If i had to come up with something for it, I'd rather see it have a personal effect. Off the top of my head, one option would be to have RA work in a similar fashion to Soul Eater, only instead of providing Hp, it would provide TP. As things are right now, this would be a welcomed effect since Pld's are constantly starved for Tp ... however, if Pld's got any other means of making up Tp (like your Tempered Will idea) this would probably be too over powered, as Pld's would literally never run out of Tp. Though, that's kind of the way War works right now, and no one seems to mind; so, maybe this would be fine.
Another option would be for RA to simply ignore the dmg penalty of Shield Oath. Comparing RA's potency to Full Thrust is fine, and RA admittedly does have a pretty hefty potency; however, that potency is consistently nerfed by Shield Oath's dmg penalty, which ultimately makes FT and RA incomparable. Pld's OT dps is actually not bad, but their MT dps is garbage. Allowing RA to ignore the penalty of the Tank stance would at least bring Pld's up a little. They would still be miles behind Drk's and War's in the MT position, but it would help. If it really bugged Pld's too much to do it, they could always nerf RA's potency a little to compensate, but I don't think it would be necessary.
In any case, these are just two ideas off the top of my head. Neither of them are required. Nor do I expect RA to go through any changes, because honestly it's fine the way it is. I only mentioned it because it's been brought up on the forums before, and when you look at all the Tank combo's side by side it's pretty easy to see that "one of these things is not like the others."