One thing that needs to be said is that on FFXIV DPS is king, in the harder fights (Savage, Extreme Primals) a tank who can maximize his damage by staying for as long as possible out of tank stance can (and often will) be the difference between a clear and an enrage, so yeah if you are not tanking you should be on Sword Oath and even if you are tanking you should also be often on Sword Oath as well, on this game a good tank is not only someone who can survive and keep the boss from hitting the party, but someone who can do all that while doing as much damage as possible.