If he had looked like in that earlier smudgy, almost sketch like picture you posted, the whole show would have been one of those "artistic" shows, where you wouldn't know half the time what you see on the screen. You can't just make one character like that and the rest, along with the backgrounds, look clear and crisp. He also had to move like he moved in his life to make him as capable. Actually he's not as capable because a skeleton is lacking mass compared to a full body, which is a huge weakness in all but the most ninja like ways of fighting, but I doubt as an undead he would be capable of learning a new style.

Gus could have been more ghastly easily, though, although that would have also made him far more unrecognisable, and thus the audience wouldn't have really cared about him a whole lot.