He's not a disciplinarian...
So? When did his players get in trouble? It seems as though you are a fan of coaches that get in your face and show their fire more so than Dungy. That is a personal opinion but that fact remains that Dungy's players never got in trouble. To call him not a disciplinarian is pretty low. There is probably not a single guy who has played for Dungy that would speak poorly of him and not do something for him.
When players lose a game and they say afterwards, "We let our coach down," that is the sign of truly a great coach IMO. A coach can yell, gameplan, do all that, but when players grasp onto his beliefs and his system and believe that he is the one to carry them to the next level and they can do anything, then I'll take that coach over anyone else.
Since when was underachieving a truly "bad" thing? He got a ring. We look at basketball and during the Jordan era, how many people never got past Jordan? Do we slight them? Stockton, Malone, Miller, Barkley, etc. Dungy ran into the Patriots, enough said.
And one last point, someone brought up winning a Super Bowl is very hard. The way they won it last year was incredible. No one thought they had a chance starting the playoffs. Remember how bad their defense was? They had the best team in the playoffs, no doubt about it. They did EVERYTHING right. You can't take that away from them and slight them because of everything else that happened.
Yes, Dungy "underachieved." But many coaches, even those coaches that you say you would take who are not HOF worthy, would give their leg to be Coach Dungy.