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

[Natsuno]

Here is the problem with the gladiator and conjure analogy. The Gladiator is an initiate of the Paladin and the Conjuror is an initiate of the White Mage. The Evoker is the initiate of the Summoner not the Arcanist. The Arcanist is the initiate of the Saboteur.

And BLM is the initiate of RAV, SCH is the initiate of SYN, PLD is the initiate of SEN, WHM is the initiate of MED... wait a sec! We're playing FFXIII-4 and I didn't even know it! :O

Although I'm still confused as to why Evoker & SMN are there.... best scrap them both. ;p

Could you stop trying to twist other peoples words to fit your own adjenda please.

On topic: As Romsa said above. Gear itemisation, mana issues... tbh, it's been beaten to death in this tread already.