Earlier quoted context omitted.
As much as our industry sucks at interviewing, it sucks at performance management even more. A congenial but mediocre developer can stick around forever in most places once they're in. This performance management weakness also makes me suspicious of various companies claiming to have nailed the interview process.
A congenial but mediocre developer may actually be more valuable than a rowdy and talented one because she pisses off less number of other brilliant developers.
But that congenial/mediocre developer is still taking up a headcount that could hold a congenial/high-performing developer instead. There is also a separate issue where mediocrity discourages high-performers.