Defensive ability, WAR VS DRK

[Reynhart]

IB is up way more often than Shadowskin or Shadow Wall, but DRK has 20% from Grit. So compare IB to Grit, DRK has the advantage.

You can't compare "Grit to Inner Beast". The WAR equivalent of Grit is Defiance.
In your example, withtout any active mitigation :
WAR : 1250 health (Defiance up) - 800 hit = 450 (36% remaining life)
DRK : 1000 health - 640 hit (Grit up) = 360 (36% remaining life)

Raw Intuition is the same as Shadow Skin regarding mitigation and cooldown, and against a boss, you shouldn't be hit from anywhere but the front.
Vengeance is the same as Shadow Wall for damage mitigation, but as a shorter cooldown.

That leaves Inner Beast for WAR and Dark Dance, Dark Mind for DRK.
Dark Mind is magic only, and most of tankbusters are physical (for now), so it's situational at best.
And for Dark Dance, it has more than twice the "cooldown" of Inner Beast (The time to build wrath, Infuriate apart), and is far less reliable.

Damage wise...It needs far more calculations, and since I don't play WAR post 50, I won't talk about it.