Infraction: Correct answer to a different question
Message to User:
Your information is correct. But he was asking about the number of targets at which it's a DPS increase to switch from single-target spells to AoE spells, not about the AoE target cap mechanic.
From 5.2.0 patch notes
In 5.3 the damage of Arcane Explosion has been increased by 40%. Does anyone know what the number-of-targets threshold for this spell over single target is now?
Area Damage Cap: The area damage cap is now 20 targets (was 10). This means area of effect damage spells now reach their maximum damage when striking 20 targets. If more than 20 targets are struck, then the total damage done is spread evenly over the actual number of targets present.