Fans bash coaches for poor performance no matter what. Capers last two years with the Packers featured injuries across the board in the secondary and that didn't matter. Fans talk about injuries as a reason for losing all the time, but if injuries happen for more than one year it's amazing how quickly injuries are no longer an excuse.
As for LaFleur, certainly no conclusions can be drawn from his time in Tennessee because of the injuries, but that cuts both ways; he shouldn't be penalized but it certainly wasn't a positive either. As I said, I think this hire is primarily about two things; first, hoping the McVay and Shanahan magic rubbed off on him, and second, that as a coach he is a definitive third in the power rankings for the front office, he presents little risk of taking power from Gute or Murphy. Fans wanted Pettine as DC and apparently so did the front office, so one of the factors in a HC hire may well have been a guy that Murphy and Gute feel confident will keep the guys they tell him to.