I don’t subscribe to one specific model but the thing is that you very rarely if ever see a group of average people achieving something great without a few outliers mixed in. In some situations the greatness of some was exactly enabled by others simply not getting in the way.
You might bring up something like Bell Labs as a counter example but my point would be that it was a large group of exceptional people and you got synergies out of putting them together but compared to the society in which they existed they were each individually outliers too.
I think to really inspect this idea we’d have to nail down what are outliers and great achievement. It is hard to judge people by anything other than their achievements (plenty of highly credentialed and well-testing people don’t accomplish much in life, right?). But, if we say an outlier is somebody who’s accomplished great things, then the idea that they show up in groups they accomplish great things becomes a bit circular.