So hiya, I'm a relatively new Level 70 Black Mage and I believe I see the easy fixes that could change Black Mage's fortune around. I need put a disclaimer though, just in case.

What I'm going to say is not confirmed for Patch 4.2 Rise of a New Sun, this is merely speculation of a man who has way to much time on his hands for a job he's fallen in love with recently.

Raid Utility:

Ley Lines: Now provides the same effect to all casters who stand in the circle as the Black Mage receives.

Mana Ward: Effect reduced to 15% of the users maximum HP, but works in an AOE around the Black Mage.

Traits

Thunder Master II: Upgrades Thunder ll to Thunder lV also when under Thundercloud, Thunder III and lV become oGCD

Those are my proposed changes to Black Mage that could change the caster around and secure them a spot within a group.