What about creating an ACTUAL Dark Knight?

[Freyyy]

Nope. I've played FF IV a LOT and Cecil doesn't do this. He casts some damaging spells (Fire - For example) but that's it.

He uses "Black Magic" hence Dark. When he becomes a Paladin he uses "White Magic" that's all it is.

FF4 is my favourite FF title alongside FF6. Like others have said Cecil as a DRK does indeed use HP-sacrificing moves and doesn't use any black magic. Cecil is also not the first Dark Knight to appear in the franchise but he was the inspiration for every subsequent iterations since he was the first to use HP-sacrificing moves (FF3 DRK had that only in its remake, the original NES one used white magic while wielding katanas, and FF2 DRK is just a title for Leon since jobs don't exist in this game).