[Maktaka]

Warlocks have a lot more for crowd control than that. Flash Powder takes out 2/3 of the crowd within 8 meters of you in an instant (for 5 seconds anyway). From the Spirit mastery, take Visions of Death of a targetable version of Flash Powder (great for archers and mages).

So a fight usually goes like:
Order in Liche King and/or lay down traps to attract enemies' attention. As they group together on approach, send out a spray of knives (maxed Flurry) with Envenom Weapon w/ maxed Mandrake and Nightshade. Keep in mind, knives group together better if you aim far away, so aim PAST the targets at the edge of the screen to get a nice tight grouping of the blades. Fire off Visions of Death* at any ranged attackers if there are any, melee troops if there aren't. Get close to the group and start pounding. If you ever get surrounded, pull back for a few steps to give yourself a moment of peace to cast Flash Powder. Repeat all the above as many times as necessary. Until everything stops running around.

When attacking targets with your melee weapon, focus more on keeping targets confused over killing them one by one. You don't have any survival traits outside of Ravages of Time from Deathchill, and that won't help against a spread of ranged fighters.

*Visions of Death is currently bugged for the better. Hit a melee fighter with this and he won't be able to engage it melee combat again. After the feat wears off, he'll charge up to you but won't attack unless he gets confused or stunned (or otherwise becomes unable to attack again).