I hope PLD gets better enmity generation on Stormblood. Anytime I get into an eight person group with a WAR or DRK, I just switch to Shield Oath. PLD can't keep up with either of them when it comes to generating hate.
Edit: I can't, anyway. I may just be playing wrong.
When tanking, you want Shield Oath on by default. The 20% defense increase alone is massive, and takes a lot of pressure off of your healer. You switch to Sword Oath when you are soloing, you are OTing for an 8-man or larger group and not actively tanking anything, or you have enough of a lead in aggro that you can switch to Sword Oath without losing aggro to anyone. If Shield Oath is up, the PLD can easily keep pace with any amount of aggro being generated.
If you are OTing, you have no need to keep caught up with the MT's aggro. Just use Sword Oath and deal as much damage as you can. If the MT dies, or you need to tank-swap, then switch to Shield Oath and then use Provoke. Provoke gives you aggro equal to the highest person currently on the enemy's aggro list, plus one point. It catches you up regardless of how far behind you are, so you never have to worry about falling behind. Just time it so you land a good aggro-generating attack such as Rage of Halone right after the Provoke. That will give you a good lead.