Class => Job => ???

[Sandpark]

they can balance this, when they change every single skill when you equip a job crystal.

for example you play the base class and all your skills are in the "class" layer. now you equip a job crystal on that class and all your skills in the "class" layer are gone, instead you get a whole pack of new skills in the "job" layer. that can be the same skills, same anmimations, same potencys, or adjusted potencys or whatever and of course new skills.
now you can balance this job without touching the base class and you can add as many jobs as you wish on that same base class.

I recall thinking the same thing before but didn't say it as simple or concise. Nice, but idk if SE wants complexity over simplification.

[Alien_Gamer]

I saw something along the line in another game but it doesn't ended up so well, I mean, everyone just equipping the "right" stuff and all content runned by same copy&paste skillset.

I've seen it succeed, I've seen it fail. I obviously can't say they'll do anything like it with certainty but based on their existing decisions with skill culling and job skills, it seems like an obvious avenue for them to try. It sidesteps the skill bloat, gives a means of customization and creates an easy way for jobs to differentiate themselves in group content. Ex: Two of the same tank, one can spec to MT with more defensive buffs, the other can spec to DPS with more damage buffs or dps can spec towards group utility or personal buffs.

I see potential in the system...but the devil is in the details and SE isn't known for their flawless execution of ideas sometimes.

[Zojha]

now you can balance this job without touching the base class and you can add as many jobs as you wish on that same base class.

And the question becomes: Why even bother tying it to the base class then?

At that point, you have effectively two separate jobs. The only benefit of tying them to a base class then is to reduce the leveling load for leveling all jobs because you level two for the price of one. You could just adjust XP gains and requirements instead, same effect.