I think the only reason they didn't give Dark Knight Cecil cool abilities is because you're supposed to get rid of him relatively early on in the game. Yes, I know you can take him up to level 99 and he won't gain anything new. That's not my point :P
I'm sure that if he were meant to be with your party in the final battle as a Dark Knight, or even if it were meant to be an option, they'd have given him something better. Dark Knight Cecil sucks by design, not by nature. Just look at Dark Knights in FFXI.
The reason I don't like Paladin Cecil as much is because he's more of a boyscout once he gets purple hair.
