No More Classes?

[Kuwagami]

While I agree with you, the Job Crystal is what changes the specific roles. For examble take the Arcanist Jobs, Arcanist by itself is a dps class, attach a SCH job crystal and now you're a healer. So if you are a THM for example and you equip the DK crystal, you will become a tank. The crystal itself can have a base HP that it starts off with etc. It's not entirely a stretch.

Without the crystal they are mere classes rather than a job. To me the crystal is what separates the two.

It's all hypothetical and the expansion will define it all.

though THM (in your example) has absolutely no tank options, where ACN has a bunch of supportive healing options (physics, E4E, virus, raise).