I wouldn't call injuries the primary reason for this team being such a disappointment.
Even just looking at their first six games before injuries to Romo, Felix, and successive injuries to Witten that really hampered him, this team was looking pretty darn mediocre. They had just lost two out of three and needed a late score to beat lowly Cincinatti.
They probably beat the Rams with Romo, but do they beat the Giants if they're at full strength? I also kinda figure that by the end of the season many players on every team are probably taking a volume of pain meds that would put most of us out of commission. I remember umpire Ron Luciano writing about how he could barely move during the week when he was an NFL lineman, and that was a loooong time ago.
The coaches being clueless and not instilling any discipline on this team are still the top reasons on my list.