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

[Shizuna]

It might be good to ask for submissions on reddit or something, probably won't get much traffic from here... I feel kinda weird being the only person not from Gilgamesh on there >_>

I guess. I'm not too fond of reddit, but I do post once in a while. I got a couple of submissions though, mostly for t13.