I don't really see it, base concept doesn't seem to tread a lot of new ground over what we have (I'm not saying you can't make it unique, I'm just saying that another heavily armored fighter with a big two handed weapons is likely going to overlap more conceptually and thematically than something like a fencer or thief would).

I always thought the easiest way to make the Dark Knight would be an offensive job for marauder (thaumaturge secondary lancer tertiary?). "Marauder" even sounds dark-knightish.