I posted this in the lore forum, but I'll drop it here as well. After much philosophical contmplation inspired by the works of Aristotle, I have come to the conclusion that the Arcanist is the scholar of the XIV universe.

Around Limsa, various people will refer to those that work in Maelvan's Gate, the customs house and arcanist's guild of Limsa Lominsa, as scholars or "scholarly types".

Like many of the FF games, they have bent the class so that it is not pathetically weak and useless in most respects. In FFIII, it was a utility class that had very little destructive power in its own right. In FFIV The After Years, the called the "scholar" a secretary - she did a bit more than just be a scholar.
Likewise, the Arcanist is a scholar and then a bit more. It is the wisdom upon which the art of summoning is founded. It is a way of making every class capable of being played seriously through endgame, much like how the conjurer is a bit more than a healing class and gladiator is a bit more than a shield wall - that is where the jobs come in.

As for the artwork of 9 characters? They're simply showing off the new features of the combat system, 8 of which are jobs.