I sort of wish players could only choose one job.

[Colino]

I have the opposite problem. A character that does everything is an impossibility in the role-playing sense.

How so? I'm not a fan of RP but surely if the world and the lore allow it than it's not an impossibility? You seem to be restricting your own RP experience by putting limits on yourself that don't actually exist in the game's world anyway.

Doesn't work like that when the game forces you to level almost every other job for cross class abilities, to even play your class optimally.

Have you even played with any jobs? You need barely any sub classes to do great with a class let alone a job (where you're severely limited as far as cross class skills go). At most you need your class at 50 and your sub at 36 or so (and don't tell me that's hard to do because we all know how easy it was to level).