He's definitely hurting both himself and the people he works with, both from the fact that he's not likely to work to improve himself, and from his depression/frustration and the fact that it's manifesting as resentment towards his coworkers. I don't mean to attack him, it's just that in collaborative work that requires skill (read: practice), a bad team member can be worse than having one too few. If it really is what he's best at, then he really needs to start practicing something he actually does enjoy, or find some way to enjoy it enough to practice.