Then it would be good to figure that out, measure that, and then at least we can put the best people on the most important projects. It's perfectly possible to imagine a world where e.g. developer IQ was the only thing that mattered and the quality of software that got produced was simply proportional to the average IQ of the developers who worked on it, sure.

I don't think that's the world we live in though. I've seen smart, sociable, effective developers fail in misorganised teams, and I've seen teams of ordinary people produce very good software by getting their processes right.