I'm at work so cant watch the video but I'm thinking Destro is your problem here, your critting will pull off of your pet no problem at all.

(I also know you aren't going to respec so I'll come up with suggestions, bearing in mind my experience is for one lock and may not scale with 5).

If using voidies perhaps keybind their taunt ability. Try taunting if you've pulled aggro (not sure how effective that would be, but worth a try).

Try using the succubus to cc a mob (yeuch). In a humanoid heavy environment so long as they aren't immune you could try to seduce a couple of targets.

I imagine you would need to have a round robin that sets your pettarget to your mains current target for each pet, and have them seduce that target. Have a macro that reseduces the pettarget if it breaks.

Seduction is pretty unreliable.

On to the best crowd control a warlock has - FEAR!!!!

If you have cleared a part of the way - work on pulling your mobs really far back into the cleared area so that they have plenty of room to run around. I would do something where you set each slaves focus to your current target (on a round robin basis). You then pull the mobs back and have a macro that fears your focus while you continue to dps down another. in some cases you can use that fear to snatch a quick bandage to restore any health lost from a hit or two.

Other than that make sure one lock puts on curse of tongues on casters. Put up curse of shadows from one lock as well.

Remember shadow ward if any of the mobs cast shadowbolts (I'm sure there are some locks in there and I know one of the bosses throws them.)