For market competition to flourish having at least a few dozen competitors seems necessary to me. People in the same business talk and run in the same circles.

For market competition to flourish having at least a few dozen competitors seems necessary to me. People in the same business talk and run in the same circles. If just half a dozen people control a market then unspoken rules can develop and signaling can be done with prices on the open market. If there are 50 competitors then active organized collusion will be necessary, like the trusts of the Gilded Age.