His dark wave is actually pretty useful, especially on the serpent road where you fight groups of enemies who can wind up doing more damage to than dark wave would. I didn't notice any huge shift in stats when Cecil became a paladin in my game. However, his cover ability proved mostly useless as he seems to never want to use it when it'd be important, and usually it only protected from weak attacks. His magic is also virtually useless. By the time you hit the end of the game you won't even want to bother with it, making it somewhat negligable.