Odd how you chose those guys to compare Garrett too, but ignored guys like Dan Quinn, Bruce Arians, and Ron Rivera. All guys hired after Garrett, and who have proven to be better head coaches.
Also, some of those guys you listed have only been a coach for a single season.
My point is... Garrett has been here as head coach since 2010.
Here's the list of head coaches who are more tenured:
Bill Belichick (2000) - 5 Super Bowl wins, 7 AFC Championships
Marvin Lewis (2003) - Its the Bengals FFS
Sean Payton (2006) - 1 Super Bowl win, 1 additional NFC Title games
Mike McCarthy (2006) - 1 Super Bowl win, 1 NFC Championship
Mike Tomlin (2007) - 1 Super Bowl win, 2 AFC Championships
John Harbaugh (2008) - 1 Super Bowl win, 1 AFC Championship
Pete Carrol (2010) - 1 Super Bowl win, 2 NFC Championships
So here's the deal... guys like Belichick are one in a million. You're likely not going to find the next Lombardi or Belichick or Jimmy Johnson. But you ought to be able to find a guy who can come in and make an immediate impact and coach these guys over the top. Garrett is unjustifiably so the 7th most tenured head coach in the league. Everyone more senior, save Marvin Lewis, has won a championship. Meanwhile we've seen relative new hire coaches come in and get their teams to Super Bowls. Yet our guy has been here 7 years, and despite getting MVP type performances from both the QB and RB in two separate years, can't advance past the divisional round. Despite having franchise QB's for six of his seven years (injury year discounted), and playing in a relatively weak division - only has two playoff appearances and one playoff win.
And people are supposed to be okay with that because.... well... we might not find the next Belichick?
If only Arthur Blank had stuck with Mike Smith (who got them to a NFC Championship, btw) because they couldn't find the next Belichick.