Our defensive problems can be attributed to two main areas. The 1st is the most obvious which everyone is aware of, our pass rush or lack there of. The fact is we don't really have a pass rush unless we're sending 6 guys at the QB, it's very disheartening. I wish I had a suggestion to fix this but I think it's more of a personnel issue which means we're pretty much screwed in this area till we can draft some natural pass rushers. The 2nd problem is our inability to create turnovers. Our secondary needs to start making some plays. When was the last time you saw a CB close on a route to try and pick off a pass? When was the last time a tipped ball was actually caught instead of going through a DB's hands? These are game changing plays and the fact is we really haven't had any since the first few weeks of the season. The one positive is we've caused a decent amount of fumbles this season, but c'mon guys, catch some freakin' balls will you?
I would add as many have said here and Nance and Simms mentioned that the Steelers had been saying that their TE's and third wideout would have big games. Meaning that the secondary after Revis and Cro can't adequately cover. I understand Coleman caused two fumbles and had ten tackles, but the secondary is just plain thin.
The pass rush just isn't there. That's not going to change before the end of the season. As for the lack of turnovers, that's the most surprising thing to me. Teams aren't throwing at Cromartie as much as we expected them to.
QB's have a pretty simple formula against us. Throw to the third receiver/TE/RB out of the backfield. We play a lot of man-to-man, so when our 3rd CB or safety gets beat, it's hard to come up with an INT. One of the virtues of zone is that you have more opportunities for turnovers, but you also give a lot more room for the QB to make plays and is too passive for this defense. The pass rush is lacking, but we still got 3 sacks. We're tied for 10th in the leage at 35 sacks, ahead of teams like Atlanta (27), Indy (26) and Baltimore (27) which everyone thinks has a better pass rush. We're above average. Would I like more sacks from the front 3? Of course. But with the quick-passing schemes these days, that is very, very difficult.
OP - hit the nail on the head. But the MAIN thing is simply no natural pass rusher. The lack of TO's can in some ways be attributed to the lack of a pass rush because QB's are rarely forced into snap decisions and throw before they are ready. I really do think for the most part the coverage outisde of Revis and Cro is adequate (not great but you can live with it) but without a pass rush someone will eventually always get open. If only Gholston was half the player you would expect at his position and spot drafted.