Honestly the only weaknesses that really should be of any concern is the kicking game and penalties the latter of which is very correctable and was corrected this last week. This defense albeit not perfect does play solid enough to actually have great QB's second guessing plays.
Yes it could be better but hell Romo could have a QB rating of 158. This defense has made a few mistakes but overall they are playing well enough to minimize the oppositions points. If Romo threw 5 TD and had 1 intercepted and returned for a TD would you be saying god Romo sucks and we need to find a new QB. Why then would you when a team is producing TO's giving the offense a chance to Score be worried about them allowing a TD or two a game.
Minus 3 games where TO's dictated that our defense had to be on the field for an extended time because of TO's or the opposing def scored on TO's and this is one of the top if not top defense(s) in the NFL. It is no coincedence that the defense has gotten better as Romo has gotten better. They are not asked to be on the field as long. The Eagles game at the first of the year also can not be blamed on the defense as much as it should be contributed to Donovan McNabb who through the first 5 games was the leading scorer in the NFL. Donovan McNabb was playing up too and at times beyond his potential during that period. Sure our defense has given up some big plays but they have also created more havoc than those TD's should hold weight against.
Also Sacks are seriously overrated stat that does not indicate a teams success. Seattle Seahawks, Miami Dolphins, Green Bay Packers, Philadelphia, Pittsburgh and Atlanta are in the top 8 of Team Sacks and they have not translated to winning or scoring reduction by the other team. Green Bay as a prime example with the fourth most sacks (33 sacks) give up 25.2 points per game as compared to Cowboys who are 17th tied with 5 others (22 sacks) but only allow 18.0 points per game.
So instead of dissecting the Defense realize they are built to minimize points and that is exactly what they have done. Stop looking at small windows and start looking at the whole picture. If I just looked at how Romo performed on the first drive or two of each game I could paint a bleak picture of his performance. I remember a game where he threw no TD passes and no one still questioned his ability. The looked at the overall performance and realized even though he didnt toss any TD's he kept drives alive that allowed us to score. Just give the defense the same chance. I am sure there will be games to come where Romo will lose and he will throw a couple picks, please understand this is part of the game and that it is no indication of how he is as a QB overall. Sorry about the rant and for being so verbose but this Defense is really good.