Many spells seem to default to this prioritization, whether they are buffs or debuffs. I'm not sure if this means the AI will prioritize hitting as many targets as possible or simply prioritize targets that literally have the most afflictions. I assume it's the latter but it's hard to tell. I usually just try to do 'as many allies' or 'as many enemies' as possible, but that isn't good for spells that target both allies and enemies, like some priest spells for example. 

 

Anyone have clarity on this or educated guesses?

It will direct the spell or center the AoE on the target with the most afflictions

that makes sense, was hoping for otherwise, thanks Myztik