A team of 8 has 28 possible communication paths. A team of 16 has 120. That is n(n-1)/2, geometry, not management.

In six years inside corporate dev teams, the calendar-time ratio of solo versus team for the same feature ran 20x to 60x. Not because the people were slow, but because the system extracts a tax that scales with its size. The day you go solo, you stop paying it.