Actually, that strikes me as a Simulationist issue (whee!).
Having a butter knife do the same damage as a greatsword has no impact on game balance; in fact, it makes for a better balanced system, since the butter knife fighter is balanced against the greatsword fighter. So it's not a problem from the Gamist standpoint. From a Narrativist standpoint, it's weird, but certainly it can make for an exciting story, and I suppose you could explore the theme of the Secret Way of the Butter Knife. It only becomes a problem when you try to imagine how, exactly, you're lopping someone's head off with a butter knife...