I find Dark Dark to be better on a Brute than a Tank.  Dark can achieve nearly the same survivability and knock the same hard caps (100 res to avoid debuff of res) it is just harder to get there.  Dark Armor has a stealth component, non suppressed, which i think works against the Tank mission and enhances the Brute playstyle.  Due to most of Dark Melee being a hard hitting ST set it does not benefit from Tank increased AoE.  Shadow Mail has always been situational, even with tanker aoe it is a long animation DoT best used for trash mobs.