As I have posted in other threads ...

The reason Classes/Jobs are boring now is because of "raid balance". The more customization given to the player, the harder and more work it takes to balance.[1]

The solution is simple.
  1. Make raids Job-only.
  2. Introduce cross-class skills that aren't tied to any class but are instead learned from Grimoires, Allagan Tomestones, ... etc. (i.e. "skill books") which are acquired from quests, vendors, dropped from NMs and appear in their own classless category - they are of course for use by specific classes only.

This way you can go wild with Classes and their skills while not messing up raiding.

[1] Raid encounters are probably designed the same way they are in WoW.

The developers build the encounter around existing Job abilities. They remove anything if it doesn't play well with specific Jobs. Damage and mechanics are designed to be beatable by existing Job abilities and such that each Job is as close as possible performance-wise.

As you can imagine, the more Jobs (and Job variations; which are from their point of view pretty much separate Jobs), the more they have to test the raid encounters against, the more simulations they have to run.