Obviously, they are not at all suited to combat, having no abilities and being poorly equipped.

And yet they can do combat:





With a sufficiently high level, a Disciple of the Hand class could run a low-level dungeon unsynced. Beating mobs to death with your tools is absurd, but it would work, and could be a fun challenge. Critically, I don't believe there are any tasks essential to progression within duties which Disciple of the Hand classes can't do.

However, the Duty Finder strictly bars any Disciples of the Hand class from entering a duty. This is understandable in the general case: handworkers are simply not cut out for running dungeons alongside actual combat classes. But for pre-formed parties with no level-sync, why not?

So, Square Enix: please enable Disciples of the Hand to enter instanced duties if in a pre-formed party!