But that actually makes the result even more significant. Class projects are heavily dependent on every student in the group pulling their part. Someone who is nice but incompetent may cost a student several grade levels, while a competent asshole may allow for them to coast along and still receive a top grade.

This is a study of MBA students. I'm pretty sure you'd get very different results if you asked CS students, there I think people would take the unfriendly genius who guarantees them an A+ on the assignment over the friendly guy who doesn't contribute anything.