I linked to as much hard evidence as I could but I'll agree that it's a little light. My hunch, just based on my own observation doing this for 20 years, is that an asshole is like a black hole of productivity, draining it from everyone else to such an extent that they're simply not worth having around, and that no matter how Brilliant they are, the rest of the team can figure out their areas of expertise with the morale boost they get after leaving (or drastically changing their behavior, though sometimes the bridges are burned too much for recovery).
Again this is mostly anecdotal, from what I've seen teams do when the Resident Jerk was fired or left. I've never in my 20 years as a professional software developer seen a single person leave a team and then see the team immediately fall to pieces because that person really was the critical lynchpin that people thought. I've seen lots of people stick around far, far too long because folks (management usually) were WORRIED that's what was going to happen, but it never actually seems to.
Again this is mostly anecdotal, from what I've seen teams do when the Resident Jerk was fired or left. I've never in my 20 years as a professional software developer seen a single person leave a team and then see the team immediately fall to pieces because that person really was the critical lynchpin that people thought. I've seen lots of people stick around far, far too long because folks (management usually) were WORRIED that's what was going to happen, but it never actually seems to.