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

[Sleigh]

SMN's DPS fluctuates very little throughout the entire fight, what word are you going to use to describe that?

No other DPS can sustain their numbers as well as SMN when it comes to dealing with mechanics or impromptu situations.
The jobs you listed are susceptible to a variety of things to make their dps take a sharp dive, such as: Dodging mechanics, running out of TP, travel time between enemies, invulnerable periods, denied access to positionals, activating the Limit Break and more.

True, on paper. However, in T10-13, BLM, who gets impacted terribly by mechanics, will still win even if targeted for mechanics (which is mainly limited to T10 Wild Charge capture, and T13 Earth shakers). That's part of the problem, that advantage SMN has doesn't bring the bonus well enough to make it win when it should, because the raw damage is too low, both from resources and from the damage (whatever the reason for this, bad stat weights, not enough PPS in their rotations, whatever, it's a bit too low, tested i135 SMN myself, pretty low compared to everyone else, very very close to BRD on a dummy) being a tad bit lower than it should be IMO.

In reality, it's more like ... no other DPS is as susceptible to boss invulnerability via phase shifts, and enemies dying too quickly, as SMN is. Those things happen more than any other job losing DPS to a mechanic.