Can someone give me an in-depth explanation why Summoner is arguably the worst DPS?

[Leonus]

If melee could do as much AoE as casters then I could see a point in saying melee ST is OP. If they fix caster single target to put them in line with melee, they should do the same with buffing melee AOE to put them more in line with casters. Anytime adds pop up in any dungeon, caster dps blows melee out of the water until it's back down to ST. Should just fix it to where both melee and casters/ranged can do the same AoE damage and single target damage. Then, no one can complain anymore.

That way anyone can pick up any dps class for anything. They shouldn't fix one end without balancing out the other.

[Minorinz]

If melee could do as much AoE as casters then I could see a point in saying melee ST is OP. If they fix caster single target to put them in line with melee, they should do the same with buffing melee AOE to put them more in line with casters. Anytime adds pop up in any dungeon, caster dps blows melee out of the water until it's back down to ST. Should just fix it to where both melee and casters/ranged can do the same AoE damage and single target damage. Then, no one can complain anymore.

That way anyone can pick up any dps class for anything. They shouldn't fix one end without balancing out the other.

OR design fights that require AOE as it should for casters to shine here and there even after being over geared for the fight? But then it's a dead end for summoner anyway since blm is too op for more than 4 targets.