The more I ponder this the more I think the split is mostly a nothing burger, and like with healers where double barrier is generally more viable than double regen, it seems to me that double "off tank" will be more viable than double "main tank". If OT is supposed to focus on debuffing and helping allies, it's quite quaint that PLD kept all of: Reprisal, Veil, Wings, Cover, Intervention, and Clemency. I love dropping TBNs and Oblation on people as much as the next DRK, but they will really have to expand the support kit of all 3 of the "OT" jobs to rival let alone be better than that of PLD's.

All that said I think the split is entirely because they wanted to introduce the parry mechanic to the new tank, and figured they need a second one and chose PLD to be that, and designate those two jobs as MT because they need to be smashed in the face to function and they don't want players to argue endlessly in casual content who should be the MT if one of those two jobs is present. Yes, we all know Damnation has thorns atp, but that's realistically sub 0.5% of WAR's DPS even when maxed out, it's cosmetic and if they delete it nothing of value will be lost.