For what it's worth, and why I didn't consider Defiance for the sake of "mitigation" in this case, Defiance's HP gains are lost each time you end up switching over to Deliverance. Now, good WARs should know when and when not to switch between these stances, mitigating the loss in "switched HP" almost entirely, but I'm going to give WAR benefit of the doubt in order to come from the worst possible situation here.

If we include Defiance as something along the same lines as Grit for these purposes, and make the assumption that the WAR is able to keep it up whenever it's needed, and that the healers have no trouble keeping him topped off after any given switch (assuming one is made), then WAR absolutely obliterates DRK when it comes to defensive values. It goes from a losing contest for DRK, to something that can't even fairly be considered comparable.