The only reason people complain about Shield Oath being at 40 with Sword Oath at 30 is because WAR gets Defiance at 30. WAR gets Defiance at 30 for a damned good reason: everything else it gets is contingent upon having Defiance active. PLD has no such requirement, ergo you need to come up with a better reason than "just because".
For leveling purposes, Sword Oath is more useful because PLD has perfectly viable enmity generation from 30-40 and there isn't any practical survivability concern; increasing kill speed will do more to make you level faster than increasing enmity or reducing damage taken. If anything, PLD needs more help with damage at that point because WAR has a very explicit damage advantage.
Furthermore, the only things this would change would be PLD performance in 3-4 dungeons (Haukke, Bray, Qarn, and Cutter's, depending upon where you're measuring from). Unless the devs are reevaluating PLD completely, I don't really see a reason to go and do it.