A big name means nothing if you don't have any success. Parcells may be overrated, but wherever he went, he made bad teams much better. The Giants, Patriots, Jets, Cowboys, and Dolphins were all terrible before Parcells came to town.
Ya and the Dolphins are still terrible. The fact is he was only the head coach for those other teams, he didn't have complete control of those organizations. Its obvious he isn't a great personnel guy.