In YC experience, 2 or 3 co-founders seems to be about perfect.
Before 20 or 25 employees, most companies are structured with everyone reporting to the founder. It's totally flat.
... but the pendulum has swung way out of whack here. A bad idea is still bad, and the pivot happy world we're in today feels suboptimal.
Experience matters for some roles and not others.
Losing focus is another way that founders get off track.
Growth solves (nearly) all problems