You haven't seen any Detroit Lions game the last, oh, forever, then. Their defense sucks. The Bills defense, on the other hand, is good. Not great, but good -- and it certainly would have been good enough to make the playoffs if the Bills offense could have scored 11 and 17 points in their last two games, respectively.
Sure, they could have more turnovers, or more sacks, or whatever, but I'm pretty sure 25 or so other teams would make the same complaints.
If you think the D is the big problem at OBD, you're crazy.