Duty finder could be more selective even if it would slightly increase the Q times.

Just because content is easy doesn't mean that groups don't fail due to the party composition. Especially in random DF groups you need every little adventage you can get.

In my opinion the light party should be limited to one support job and full party to two. It wouldn't also hurt if every job could be only once in the light party and twice in the full party. For the premade groups' sake allow them to ignore this limit, but don't put another support to the group when there are already two in the premade one.