I tend to not be the reactive type of fan, but I've had enough of Ron Gardenhire — I do not believe he is the right manager for a rebuilding team.
To check my biases, I decided to look back over his Twins tenure and see how well he did developing young major leaguers.
My method — for starters and position players, Gardenhire gets a +1 if:
A. The player arrived at Minnesota under the age of 25, unless the player had more than 2 years of partial experience in the Majors; and
B. The player had more than 5 WAR for Minnesota, either by the player himself, or by players the guy was traded for.
For relievers, the standard is lowered to 2.5 WAR -- I don't think WAR does a great job of evaluating relievers.
2002 — +6 (AJ Pierzynski, Bobby Kielty, Michael Cuddyer, Johan Santana, Kyle Lohse, Juan Rincon)
2003 — +1 (Justin Morneau)
2004 — +4 (Joe Mauer, Jason Bartlett, Jesse Crain, Matt Guerrier)
2005 — +2 (Scott Baker, Francisco Liriano)
2006 — +2 (Pat Neshek, Glen Perkins)
2007 — 0
2008 — +2 (Denard Span, Jose Mijares)
2009 — 0 (team traded away Carlos Gomez without getting value).
2010 — +1 (Trevor Plouffe). Note, team traded away Wilson Ramos & Ben Revere without getting value.
2011 — +1 (Anthony Swarzak).
2012 — +2 (Brian Dozier, Eduardo Escobar (bloomed after Gardenhire left)
2013 — +2 (Ryan Presley, Kyle Gibson (bloomed after Gardenhire left)) Note, team traded away Aaron Hicks without getting value. Hicks was worth 0.8 WAR in 2 seasons under Gardenhire.
2014 — 0 (Jorge Polanco got 8 at-bats at age 20. If you want to count him, that'd be +1)
Gardenhire started very, very strongly at developing young players, but dropped off a cliff after 2006. Worse still, (very good) prospects like Aaron Hicks, Carlos Gomez, Wilson Ramos & Ben Revere all were traded by the Twins without getting value.
You may ask — shouldn't those bad trades be blamed on the General Manager and not Gardenhire? Perhaps — but, except for Gomez, none of those players played well for Gardenhire, and he certainly didn't quit over the GM deciding to trade Carlos Gomez, or Wilson Ramos.
The evidence that Gardenhire can develop young players and build a championship team comes from 2002-2006. Since then, he has not developed young players. As a result, Gardenhire has finished way below .500 every year since 2011.
It seems that Gardenhire was once the right manager to develop a very talented and very young Twins team (the 2002 team also had Torii Hunter (26), David Ortiz (26) and Jacques Jones (26)). Whatever development talent he may have had has been gone for a long time now.
The Tigers have torn down — now they need a manager who can rebuild. Gardenhire is not that guy.