Rogue (or whatever they choose as name) give you the weapon skill for use 2 blades at the same time:
- Thief, teach you the art of steal
- Ninja, teach you the use of the ninjutsu.
your skill with the dual wield will come from the rogue class while your jobs will give you more...specialized skill.
now, you mark a point when you say that jobs are hard to differenciate from the class, and that the main reason i think they need to add more level before add new class and jobs. for give to the jobs more skill and make them really different.