That doesn't sound so much like a brilliant jerk as a midwit egomaniac, which are pretty common on the ground in programming. I've worked with people like that too, and what they're really doing under the guise of making your code better is rewriting modules because it's less trouble than figuring out how the existing code works. Invariably they break something in the rewrite, too, because they didn't understand the full scope of the problem domain (which, circling back, is why they didn't understand the original code).

And of course when you assign them to solo projects they fail. Because they're not very good at software development.