Does it matter with the rosters that they've had? When Garrett took over mid-season for Wade, they still had Bigg, Gurode, Barber, Roy Williams, Sensabaugh, Felix, Bradie James, Keith Brooking etc...etc..
They could only rebuild the roster slowly due to salary cap limitations.
Also, the team mentality that Garrett inherited was terrible. Wade took a good roster from Parcells and let it deteriorate into a bunch of over entitled, over paid underachievers. Garrett as OC was the one that stood up to TO because Wade wouldn't do it.
I don't know if Garrett will ever win, but if he does get replaced, the talent, team mentality and salary cap will be in a much better situation than what he inherited. That's how it worked in SF. Mike Singletary wasn't quite the right guy to win, but he did instill a sense of discipline in the team while their GM put together a quality roster. Harbaugh came into an excellent situation with both talent and a decent team mentality.
If Harbaugh had become the Cowboys HC instead of Garrett, I still think it would have been a long time before they were Super Bowl contenders. He might have won an extra game per year, but they wouldn't have been Super Bowl contenders.
It would probably have been faster to start with no talent and no big contracts than the situation that Garrett inherited. The over entitled guys could all have been eliminated immediately and he could have signed many players in free agency that fit his RKG mold. They would have been 4-12 or 2-14 the 1st couple of years instead of 8-8 which would have been a big benefit in getting top 10 draft picks.