Evaluating coaches is tough because so much of their performance has to do with the owner, GM, director of player personnel, scouting, and injuries. In spite of all that, I do firmly believe that Tony Dungy is over rated as a head coach. I think that with the players he had in Tampa Bay, that team should have annually made it deeper in the playoffs when he was there and probably should have gone to the SB a couple of times. His game decisions tended to be overly conservative and though his players profess their love for him, they seem to come up unfocused and poorly prepared more often than not. That Buc team won less games than the year before for three straight years, but as soon as he's gone they win the SB? Dungy is given credit for turning around that franchise, but that is more due to a change in ownership and Jerry Angelo than Dungy. Don't forget that in Dungy's last three playoff games with Tampa Bay, his team did not score one single point on offense. Zero points in three straight playoff games!!!!
In Indy, he walked in to a head coach's dream: a very good team that had just under acheived with a terrible won - loss record the previous season, with good players added to the roster. The team had nowhere to go but up and had a roster that included one of the leagues's best QB, RB, and WR. It would take an incredible amount of futility to screw that up.
On the other hand look at Jeff Fisher. The team was not very good last year, lost several players to free agency, was not in a good cap position, and was expected to be one of the five worst teams in the league. In spite of that, he gets the Titans to the playoffs; to me that's a very good head coach.