PLD's Shield Oath reduces damage by 20% which scales as you play harder content. I.e. You get hit harder but you mitigate more.

WAR on the other hand doesn't scale. The amount you self heal is the same for easier content. So what needs changed?

Probably better scaling the self healing to keep the Warrior tanking method. Problem is how would you do that?

Maybe The % of damage parried will be healed with defiance? Which doesn't sound like much but in theory it doubles your parry strength while linking it to the warrior style or tanking.

Healing buff with wrath should maybe be static with defiance?

Or create a "Rage" stack - when you are hit with critical damage these stacks which can be used to increase healing power from actions. I.e 1 stack increases Inner beast and Bloodbath by 10% 2 stacks 20% ... 5 stacks 50%.

Just some thoughts =]