If anything I still don't understand one thing: 19 jobs, and yet you can't change yourself in a dungeon when you actually or should need it.

How many times have you lost a tank, or a healer, and decide "Okay I'll go X or Y" but the game says "Nope, you're out of luck" because..."shrug"

Kinda makes this whole system off when you can't even change jobs/classes when you actually need. And when you can, it's heavily punished.

Might as well stick with one job in this case.