Buck Showalter managed the New York Yankees from 1992 - 1995. He was great at building a talented roster of players, but was unable to get the team to play championship baseball. After he was fired in 1995, the Yankees hired Joe Torre, who promptly won the World Series with the 1996 Yankees with the team Showalter built.
Buck Showalter managed the Arizona Diamondbacks from 1998 - 2000. He was great at building a talented roster of players, but was unable to get the team to play championship baseball. After he was fired in 2000, the Diamondbacks hired Bob Brenley, who promptly won the 2001 World Series with the team Showalter built.
Showalter was a 3x AL Manager of the year, primarily because he was able to turn around bad teams. But he never won a championship.
The Cowboys owe a debt of gratitude to Jason Garrett for changing the team culture. The mindset to build through the trenches, and in the draft, rather than focus on making splashy free agent signings for skill players has fundamentally changed the way the Jones family has approached team building. But like Showalter, Garrett has shown he doesn't have what it takes to get to the championship level when it comes to being a coach.
If I was a team like the Dolphins, I would jump at the chance to hire Jason Garrett because he has proven ability to change the team culture, and establish a program to successfully build a talented team. That is a valuable quality, and well worth hiring Garrett for other NFL team turn-around projects. But he's simply not a championship level coach. As much as I've defended him over the years because of the task at which he was working, the reality is that now that the team is ready to win, he doesn't quite know how to get them over the hump - just like Showalter.
