You make a decent argument above; I actually agree with a few of the things you said, in particular about the winnable games. There were games were I feel Garrett should accept completely responsibility for the loss. But there are few things I would point out. One, Ware played injured throughtout the year, perhaps being a detriment to the team as a whole, though he still had decent stats. Two, conventional wisdom of the 43 is ideally you can send players in waves. Their ability to do that last year was considerably hamstringed by the lack of talent behind the starters. Three, Selvie, Ware, and Hatcher, the significant contributors of the line often times were a tale of two different palyers. They were inconsistent, allowing QB's too much time in the pocket, which afforded them the ability to pick our secondary apart - granted, much of that was likely due to them being exhausted - see point 2. Four, continuity - the defensive line's make-up was constantly having to change as a result of injuries. Five, teams do overcome certain injuries, but not typically the loss of their starting QB. Romo play's that final game, who knows, we may actually have made it to the playoffs...especially considering that loss was the only loss the Cowboys had all year in the NFCE. Six, what was truly odd about last year was that the injuries on defense seemed to focus right smack in the middle. The 1-tech DT, MLB and Safety. I'm not going to say that middle of your defense is the most important part, but when an opposing offense needs a few yards, that's typically the place they are going to hit. And finally seven, the 43 was on it's maiden voyage, so-to-speak, so some growing pains with many of the players converting to new positions was expected.
I'm sure there are others reasons to look at, but injuries did play a huge role in the epic fail that was last season for the Cowboys defense.