Even if there wasn't an indicator, but a way to target AoE precisely in center of mob group rather than, for example, AoE spells which "deal damage to enemy and enemies surrounding it". It's pretty impractical, because you might have two mobs far away from each other such that AoE wont hit both if you target one of the mobs alone, however, they aren't so far away that if you aimed AoE at midpoint between them, it would actually hit both.

So it's more annoying in that regard than anything else.