Unfettered freedom to move and use oGCDs "barely matter"? To a tank?
I was talking in a general trial/raid situation, I dunno about you but I barely move since the boss just positions itself anyway but even if you can position the boss it keeps getting stuck between attacking and moving.

Why wouldn't it be able to use oGCDs?

GNB has no casts. It has only abilities and weaponskills.

Paladin has spells but no cast times, as of ShB.

So where would that finger point in this regard?
How did you even jump to this conclusion? I thought you were talking about the fantasy of the tank role, I even gave my little headcanon as an example. But really, why would mitigation effects seize to function? I still get blocks when I'm casting Clemency, so what were you getting at because I'm confused.

I'm referring to literal dodge chance, hence it's pairing alongside block and parry, neither of which are actively performable on DRK (heck, the latter isn't actively performable at all, as of Raw Intuition's change).
So why are you bringing it up?

Perhaps this is a difference in nomenclature. When I hear "caster" I think a job with at least a significant presence of and concerns surrounding cast-times, just as in your later use of the term. So when I hear that you want to turn DRK into a "melee caster" with "cast timers" that is what I think of, and it does not then sound fit to me to be a tank, at least in the present context of the game (whereby, unlike in WoW or the like, there are no mobile casts and one cannot use any other skills simultaneously with casting, and casting forfeits all RNG-based mitigation).
I'm not married to this idea, I was just spitballing and hoping to get some people to think along but like usual negativity wins and we're talking in circles like old contrarians.