3 years is not SOP around the league? Huh?
For every Jason Garrett, there are several Jeff Fisher's, Gus Bradley's and Dick Jauron's. The argument that firing a defensive coach who can't coach defense after 2 years would poison outside coaches is ludicrous. Do you think Cowher, Gruden etc etc are sitting at home watching that Steelers game and saying, "the Bills better keep Rex, he's got a good thing going?" No chance.
Rex ain't a young college guy learning on the job. If it was a younger guy, you expect growing pains. Rex is a 7 year veteran HC who has lost the locker room. 9/10 HC's understand he's done.