According to Price's Law 50% of the work is done by the square root of the number of people. As the amount of stuff you need to do grows linearly, the amount of people you need to do that stuff grows exponentially.
I am curious to see how Red Hat performs now that it's been swallowed up by IBM.
I could only find this study (admittedly from 1986) that disproved the original hypothesis - https://www.sciencedirect.com/science/article/abs/pii/030645...