I think this is too simplistic.
This friends-from-school partnership seems to have worked out well:
Obviously, hiring friends, like working with a spouse / S.O., adds several extra elements.
But strength can come from many vectors.
What doesn’t work well in my observations and experience is hiring friends mainly because you already know + trust them. That sounds good, but the problem with that is you tend to ignore their other weaknesses. That’s somewhat akin to hiring just for domain expertise. It’s not enough to make up for not also being great at the role.
Yes, if you hire friends you may lose them as friends. That is a real risk. But successful start-ups are all outliers. Hire the best possible people you can find for every role. Friends included.