As a PLD, in relic + 1, average ilvl80 gear, I generally run AK and WP bosses in sword oath. I sometimes switch to Shield Oath if the healer looks extremely under geared as a safety.
I think it's extremely situational, but I wouldn't assume because a PLD isn't running Shield Oath, that means he isn't doing it right. It's a tradeoff between dealing extra damage or taking it. You have a lot of liberty with that in AK and WP.
If the tank is losing aggro, or taking too much dmg, I think at that point it's perfectly fine to ask him to throw his defense/health buff up, but if you're comfortable healing, then it's an overall benefit to your party to have your tank dealing a significant more amount of damage than he would otherwise.
