You are missing half the equation when you say "stability". There's also the component of success.
Let's compare:
- Garrett has been head coach for 6 years (I won't count the interim year). He has 2 playoff appearances in 6 years and one playoff win in 6 years.
- Seattle with Carroll. In Carroll's first 6 years, they made the playoffs 5 times, made two Super Bowls and won one of them.
- Green Bay with McCarthy. In McCarthy's first 6 years, GB made the playoffs 4 times, went to two NFC Title games and won a SB.
- New England with Belichick. In his first 6 years as head coach in NE, they won the SB three times.
- Pittsburgh with Mike Tomlin. In his first years as head coach in Pittsburgh, he made the playoffs 4 times, made the SB twice and won one.
- Pittsburgh with Bill Cowher. In his first 6 years as head coach in Pittsburgh, he made the playoffs all 6 seasons, made the AFC title game three times and lost a SB to the Cowboys.
So no offense, but when you try to cite stability as a strength here and then try to equate Garrett and the Cowboys with these other franchises and their coaches, you lose credibility here IMO. Those are horrible examples and if anything, undermine the point you were trying to make. Those franchises kept their coaches and stability because the coaches showed high levels of performance right from the start.
If Garrett can't push the franchise further next year, and win a playoff game or two, then I don't see how one can continue to argue that we need to keep him for "stability".