Tire Rotation

A year ago I had to get a replacement tire on Christmas Day when I experienced a flat. The brand of the replacement was a Cooper. The existing set on my car are Michelins. When I had my car serviced recently which included rotating the tires, only the two Michelins on the right side were rotated. The Cooper and remaining Michelin on the left side were not. Should I get a new Michelin tire to replace the Cooper despite the difference in wear with the other Michelins’?

Do you recommend any other course of action for maintaining tire wear with my current 3 Michelins and one Cooper other than what the dealer did as described above?

Thank you for your time and assistance.

Paul Burnam