question about gunner class.

[Allyrion]

So far it seems that the ranged jobs fill in that support role in FF. Probably because their mobility. They can still attack and move, unlike casters.

There's also the description of Astrologian.

And for the Astrologian? What makes this class different from say the White Mage?

This class has the capability to drastically change your current stance. This class has the ability to draw cards and depending on what card you get you can buff your allies or support your party members. It’s a very different mechanic compared to the Scholar or White Mage.

Not sure about DRK, but support seems to be a theme with the new jobs.
SCH has somewhat of a support role as well, so ranged and healers seem to have fit support well.