Sorry but this is Final Fantasy not some terrible korean F2P mobile game. Having different skillsets every 10-20 levels is a pain in the ass and doesn't make sense for balancing jobs with any form of continuity. So you're a level 80 Dragon Knight but then you do a level 70 primal and you get bumped down and now you have a different skill set?

The only FF game that had "prestige" classes was FF1 and it was a straight upgrade that kept the continuity of the base job but added better stats/equipment and added magic (in case of Thief->Ninja and Warrior->Knight). The classes in FFXIV are named such for a reason based on the lore and story surrounding them. It makes no sense to unlock Dragoon at level 30, with the entire story and all the NPCs referring to you and others as Dragoons but then not officially being called a Dragoon till level 80, and then it changing to Sky Rider or whatever later.

If anything, I can see the job crystal evolving visually or bestowing better stats, but at the end of the day, it's a piece of crystal that carries aetheric imprints of past wielders of our jobs, which when we listen/view their lives via the echo (never shown, but is inferred), we learn long-lost spells and techniques in a manner of days/weeks instead of years/decades it would take to learn them naturally.