I’m also playing warlock, but low-life and some different skill choices.
Defenses - what is your normal HP and normal ward? You look to have a good amount of both, but Endurance doesn’t help ward, and neither does life leech. So I suspect a lot of your gear affixes and passives are wasted a good amount of the time. Looks like your EHP is 6k, and closer to 4k vs DoTs - that isn’t much my build will be about double that. I think it is most effective to focus on HP/endurance OR ward - not both. You also need to get some “Reduced Bonus Damage Taken From Critical Strikes.” Even 50% helps a ton.
For offense - what are your main damage sources? Fire? necrotic? Spell hit or DoT? based on skills/passives I think it is DoT as I see 2 overloads. But your Ladle has T7 Spell Damage? That needs to be DoT imo.
For gear - why mortality’s Grasp? You already “mark for death” via bone curse. Replacement depends if going pure HP or ward. Pearls of the swine is great, but you really want the Decrepify one, 15% more DoT is a ton. The rest depends on low life or HP focus.
if you make him down to 20% i guess you always die to his last big black circle area.
the trick is to be able to ran away fast enough, the animation is always the same, he charge is flay above his head a long time making circles and then slam the ground.
you have to be at the limit of the safe area and wait for when he hit the ground and get the hell out this place when the circle expend. you need some move spped of a traversal skill, look at hit like a circle, you need to be as far as possible so go the way there is the more room possible. Sometimes, if the fight ran poorly you got stuck near an edge of the area and there is nothing you can do to dodge the expending area.
We can look at OP’s profile 16 months after the original post to see their warlock wearing Null Portent in CoF, from this we can assume OP was able to beat abberoth.