Most of Affliction warlock's strength in Mythic+ is due to the prevalence in power per
Frammenti d'anima utility. Before, you would use a single
Frammenti d'anima to cast a single
Afflizione Instabile on one target. Not very impactful, except for focused single target damage. Your only real AoE choice was to spam
Seme della Corruzione.
Now, with the addition of
Estasi Malefica, you now have a strong nuke that hits every single target affected by your DoTs. To break down what a quick AoE pull could look like for an Affliction Warlock now, with no major cooldowns, you can throw a few
Agonias out, cast one
Seme della Corruzione to apply
Corruzione to everything, cast
Contaminazione Vile, then spam
Estasi Malefica until you run out of shards. While this may not be the most ridiculous AoE output of any class (see Destruction Warlocks), it's essentially available for every single pull. In addition to this, Affliction is typically known to be one of the best scaling specs in the game - with endgame level secondary stats, it's no surprise that a spammable AoE nuke has nudged Affliction into the limelight.