Shouldn't look at the defense like that. Consider this. We only had DG in half our games last year. I believe we were 6-2 in that stretch. In the stretch without DG we were 5-3 season (with a playoff loss 5-4). However over that stretch, Derrick Rodgers was also injured and Zach Thomas was like at 75%. Both Ernest Grant and Jermaine Haley were battling injuries with Haley not even able to leverage himself properly...Kenny Mixon had lost a bunch of weight and wasn't looking even as good as he use to at stopping the run.
So take the 2nd half of the year as baseline. Went 5-4 including playoffs. Now we've got Larry Chester which is a massive improvement on the injured Haley/Grant combo. Behind him we've also got the now healthy Haley/Grant combo to keep people fresh. Zach healthy. Derrick healthy. Morlon better. Rob Burnett, Jay Williams, and David Bowens at LDE (which is supposed to be meant as a strength, since I believe Burnett plays better than Mixon...perhaps not Williams though, and I'm a true believer that D.Bo is AT LEAST as good as Brommell). And perhaps most importantly, we've got a Jim Bates who is willing to toss Arturo Freeman into the box more to stop the run.
By the way, you DO realize that if you take the last 2 years worth of games, the difference between DG being in at DT and DG not being in at DT is a mere 7 yards per game rushing...