DM/SD Brute could possibly be the strongest single target attack character in the game (when fighting in groups). But because it is mainly single target damage, don't expect it to conquer over your SG leader's FA/SS Tanker in terms of killing speed.
I think the top attack chain is either Smite-Siphon Life-Smite-Midnight Grasp-repeat or Smite-Gloom-Siphon Life-Midnight Grasp-repeat.
-Shadow Punch is a useless power. Smite does around 35% more damage at only a 12% longer cast time.
-Depending on what you're doing with this character, True Grit is worth slotting for.
-Blessing of the Zephyr set is pretty useless for you. You're softcap, plan to use Darkest Night and you're immune to KB thanks to Active Defense.
-Slot Dark Consumption for endurance. Even with Fury/Soul Drain/Agaist All Odds at max targets, DC's damage is below par.
-Phalanx Fighting can be used as a mule for LotG 7.5%, Kismet or Shield Wall uniques.
-Make Soul Drain perma.
-Swap slotting between Weave and Grant cover. Weave is a higher end/sec power, Cystos Hami-Os would workout better in that.
-Adding Explosive Strike to Shield Charge can change the knockdown ability of SC into a knockback. You may end up chasing enemies, putting enemies out of AAO/Soul Drain range.
-I wouldn't slot One with the Shield for much. It can only be active 1/3rd of the time. Also it is unaffected by recharge so the recharge portion of the heal/damage resist IOs are doing nothing.
-Slot Gloom with Apocalypse or 50/50 Apocalypse/Devastation for a lot of HP/regen.
-Make Hasten perma.