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

[Truedragon]

Deal with it. People are getting real tired explaining the same thing to you over and over again. There is no big mmo out there that has a caster/ range outdamage melee dps anymore. So if you dont like being outdps'ed, then change your class to a melee.

The days where Samurais, Dark knights, Warriors, Dragoons, Monks and Thieves sat at the sidelines while SMNs and BLMs nuke everything from Kirin to Absolute Virtue...those days are long gone.