Face it, in this era where the rules favor pass happy offenses, maybe the idea of a dominating defense that can consistently hold an opponent to the teens or single digits is now antiquated. I think it was Aikman that said he would pick a great offense in this day and age to beat a great defense, and so would I (eg the Pats over the Steelers last night).
From what I've seen in the league so far, even most of the good defensive efforts that I've seen have been more a product of bad offenses (and there are plenty this year) than good defenses. The most complete football team I've seen so far in terms of balance are the Colts, but with the loss of Freeney I'm not even sure that's true anymore in an absolute sense.
I guess I can live with the Cowboys having a mediocre defense against good offenses (and there won't be that many in the playoffs) if they can continue to have a great offense that can put up 30+ points every week. A rematch with the Pats should be another shootout, and will come down to which defense can get those 1 or 2 critical stops when they are not giving up touchdowns.