Job advancement wasn't something that was rare in this world. On the contrary, almost every single expert who had reached a certain level would choose a job suited for them to advance to.
For them, it was a necessity upon reaching a certain level, while in my System interface, there was a much more direct view on it.
LV60 Warrior/LV7 Weapon Master; LV60 Justice Knight/LV2 Castigator; LV60 Mage/LV1 Fate Weaver. The former were the basic jobs whereas the latter were job advancements. For the basic job, one would have to continuously temper oneself and mature through the Iron, Bronze, and Silver ranks before they could reach the standards required for a job advancement.