That is simply not reality though. Sure, we fire Garrett after 2015, hire, say, Dirk Koetter, even if he bombs in 2016 (a year where Garrett succeeded given the talent he had), and goes maybe 8-8, he's not getting fired after one year in favor of the available-because-he-wants-to-get-back-to-coaching Jon Gruden.
You are gonna get stuck with a newly hired coach for a number of years just because of the contract they sign and because PR will mandate that you don't change coaches on a whim. It's the same reason -- unfortunately -- Jerry never would have considered dumping Garrett after 2014, 2016, or 2018. Because they were fresh off Divisional Round playoff appearances. Despite the fan anguish about underachieving he just never was gonna dump a coach that he hired when it looked like he was possibly about to take the next step.