I disagree, somewhat :-) There are people whose contribution is horrible but it's rarely confined to the quality of their code. It's more about being able to lead the company in directions that are ultimately wasteful in some way or other and not being able to change direction when the time is right. That leadership may be expressed in code, but the code is as much or more a symptom than the root cause.

With basic QA practices in place (peer review, coding standards, designs grokked by teams not individuals etc.) a single person usually can't muck up the codebase very badly. He or she can still poison a whole project or company.