Ahh, the smell of elitist bile in the morning.

Honestly, the role of a job and how to play it is not learned through gradual leveling. It's through trial and error doing the actual event in question.

A Dragoon trying to deal as much damage as he can in a chaotic XP party ain't going to know jack about any event, be it a Primal Battle or a Dungeon Raid.

And learning Black Mage is as simple as "Watch your hate, press buttons 1-3, press this button when high on hate, and this button when low on MP."

The rest is gearing, which you don't have any reason to gear well until endgame anyways, and fast leveling expedites this process.

So no, get real. Leveling is a grind. It does not improve the skill of players. Practice at the actual event in question does.