If you consider Shield Oath and Grit, you have to consider Defiance, too. And since they mostly give you the same eHP, it's much easier, and not very relevant, to ignore them.
Or else, you have to convert every mitigation into eHP, which is not doable with Hallowed Ground, since it gives you "infinite HP" for its duration.
Yes, you're right, a WAR (or a DRK) shouldn't focus all on mitigation, and so is DRK. The problem is that, if they chose to, they could outdo PLD. On the other hand, if PLD decide to focus on DPS...they'll still be far below WAR and DRK. Oh, and by the way, even when focused on mitigation, WAR and DRK will also do more damage than PLD.
And remember, that, in your adjusted mitigation numbers, you still didn't include Holmgang and Walking Dead