So BLM as AOE covered, MNK has single target... What does SMN bring?

[Akiza]

The Summoner doesn't have sustained damage because their damage starts out high then declines over time. The Summoner's issue is it has diminishing returns on dps throughout the fight.

The Black Mage is more sustained damage then the Summoner because they're around their min and max dps potential in long encounters while the Summoner starts at max then rolls down to their min value the entire course of an encounter. Even dps simulations show that in a shorter encounter Summoner has the highest dps while in longer encounters Summoner's lose around 80-100 dps.