Who would you argue should have gotten a longer leash?
After Fontes they gave Ross 3+ years and canned him after going 27-30. Let Moeller finish out a dead season, then hired Mornhingweg who went 5-27 over two years. Then brought in Mariucci who went 15-28, to be fired for Juaron to be interim and go 1-4. Gave Marinelli three yers to go 10-38, then brought in Schwartz and gave him four years to go 29-51. Caldwell got 4 years and went 36-28, but no one has ever argued Caldwell is a good head coach and if you want to argue that, your feet are kinda out from under you.
Which is to say nothing of the fact that you're kinda missing the point - the ownership let's the front office handle that stuff. They're very well known for staying out of stuff. So even if you think that's too much turnover - even though it's pretty typical for an NFL franchise - it likely wasn't ownership making those calls. They are one of the most hands off ownerships in the league. You can perhaps argue that that is to their detriment, but criticizing them for coaching changes - when in reality, it's more likely GM issues over the years that have kept them in the doldrums - seems either foolish or uninformed.