It's in the broadway performer's best interest to give his best effort(for he'll want people to keep paying to come see him sing) and it's in Mike Brown's best interest to put the best product on the field that he can.
But is it an ethical lapse if he doesn't? I don't know if I'd go that far. So long as there's no false advertising involved. (ie A broadway theatre tells you that Hugh Jackman is going to do his one man show, but really it's the Hugh Jackman from Brooklyn who just wipes his nose for 3 hours) than I don't think there's any lack of ethics.
FWIW, I think Mike Brown puts his best effort into putting the best team on the field. However, I think his best effort is constantly constrained by his inability to objectively see what is best for the team.