Warlocks & Anub'Arak

Affliction vs Destruction
Depends on the strength of your cleave AE. SoC spam will get you your highest position on the meters but may be a waste of your time if the adds are already dying at a quick enough pace, i.e., before the next wave spawns. My expectation without seeing logs, comp, etc. is that you're better off focusing Anub and helping with SoC/corr spam depending on how far behind you are on adds. When p3 rolls around, it is almost certainly the best use of your time to DS Anub exclusively until the end if possible, seeing the damage done to a target <25% is rather crazy as Affliction, compared to Destruction..
Meaning that you will be most valuable pushing 8k single-target DPS in p3 and around 5/6k during p1 & p2. While destruction would have mana issues with SoC seeing RoF isn't high enough DPS.

My opinion:
Spec Affliction using a Fel Hunter instead of a Succubus, keep up the 3 DoT's & Haunt on Anub during the entire fight, SoC whenever you have Corruption on 2 or < targets, in p3 solely DPS Anub using the rotation that follows:
Haunt > Corruption > Unstable Affliction > CoA > Drain Soul (Filler) > ... and ignore the adds.

In some videos ive seen, the warlocks were playing demo, using immo aura + shadowflame when adds were up, while nuking boss. How come youve not given that a look-in?

They only did that because of the lack of 4 pieces T9.5. Doesn't even come close to Affliction