With Warrior being so squishy..

[Keldon]

Hummm, Defiance also reduces damage by 20%... always has.
From the official job guide:
"Increases maximum HP by 25%, while reducing damage dealt by 20% and increasing enmity. Increases own HP recovery via healing magic by 20%."
Only reason for WAR to do more damage in tank stance is unchained (which is now a no no), Upheaval and IB ignoring the damage penalty.

I'm assuming you read him wrong: Shield Oath makes the paladin take 20% less damage, while also dealing out 15% less damage. Defiance gives the warrior +25% hp and +25% healing received, while also dealing out 20% less damage: it doesn't reduce his damage taken at all, it gives him more hp/healing instead.

Or whatever the exact % are, I'm not at my home computer to check right now.