Where does it say jobs are a set of quests? I've not seen this information either.

From what Yoshi has said regarding jobs they don't have a rank or a level associated with them, they don't progress. They are supposed to be a more restrictive skill set for a class designed to be used in parties. As such, archers who have bard can either play as Archer, or they can play as Bard, either way they gain levels for the archer class.

If anyone has seen information contrary to this, by all means, please share.