Injury is one of four main reason. Stafford regression in the redzone, turnovers, and unexpected bad DE play.
All can be fixed. Three without roster moves. Stafford/turnovers/injury
You keep pointing to these things, but here's the reality shared by many others:
1. Injuries happen to every team. Other teams overcome them and the Lions did overcome them in 2011. In 2012, the guys who were supposed to step up did not. Then the Lions started street guys. Not Mayhew's fault that he had no alternative to some degree, but the lack of depth is something that might not have been an issue if he had drafted better.
2. Staff regressed or teams figured out the Lions RZ offense? Or maybe Staff had his career year in 2011. You cannot guarantee his 2012 season was the fluke. This will take several more years to determine. Much of the blame here I place on the coaching staff, for they needed to really work harder on his mechanics, reads, and develop new plays so the D would not have the Lions so easily figured. If none of those things are corrected, then there is less hope that 2012 was the off year.
3. Turnovers sucked and that can be an anomaly any year. However, they can also be difficult to correct. On this front, it does seem the FO is making changes. Still, as with #2 above, if Stafford is not given better coaching and really works to fix what went wrong, his INTs will likely not change all that much.
4. The poor DE play may have been unexpected by you, but others anticipated it. KVB being older and Avril having been exposed against the run were things many had pointed to as potential problem areas before 2012 began. Many wanted Avril gone instead of tagged, most of them wish that had happened. However, the poor play of the backups was not anticipated by this same group, many believing the backups had the ability to step up. That did not happen and proved to be a big problem that without doubt must be corrected and I think it is agreed we all look forward with anticipation as to how Mayhew will try to correct it, whether in FA, Draft, or both...hopefully both.
In the end you are still making a large number of assumptions and have too many IF scenarios to provide any comfort or calming of frustrated fans. Personally, I cannot wait for FA and the Draft to be done so I can look at the new roster and once again return to being an idiot drunk on Honolulu Blue Kool-Aid! Cuz that is how I roll (some said 12 wins going into 2012, I was saying 13). I go into every year as one of the biggest HBKA drunks around. I guess my problem is I got too drunk going into 2012 and this hangover has been a bitch. lol