This is a non issue.
For starters, Im gonna hazard that caster AoE probably does more damage compared to melee potency (which requires a combo typically, outside of oGCD which either have long CDs or cost mana). IIRC, potencies are not 1:1 across classes. An 800 damage potency on a BLM is not gonna be the same as MNK.
Furthermore, if the end result remains unchanged, and there is 0 impact on gameplay, then this complaint is pointless. In the rare occassions where you run out of mana, that AoE pull mustve gone on way to long to encounter that.
It's a non issue and assumes that the devs are so incompetent about balance that they cant see something so clearly as Casters still expend mana while melee dont without balancing for that aspect.