There are two types of "statistically great" defenses in college football. One type is the one that is loaded with 4 and 5 stars who are well coached and disciplined. I.e., they are actually great. The other type is the type that cooperates with a moderately decent offense and gets into a bunch of slug fests that might go either way. This is the Iowa, Wisconsin, Mississippi State, Iowa State, Stanford, Penn State, Michigan State model. Don't get me wrong, all those ball clubs have good defenses and some really talented players, but God help you if you leave them on the field all day in bad spots.
Look, you can point to games like Alabama, but Tua was hurt when they played that game and Nick didn't let him run and called off the dogs the moment it was apparent MSU wasn't going to be able to score. At the end of the day, when you're lining up to play one of those teams, you ain't game planning to get into a high scoring shootout.
And now I don't want to take anything away from the offense because the interior of their d-line is right there with anyone, but 2 of our TDs came on really short fields and 3 of our points came courtesy of 30 yards of penalties. But I don't think for a second that MSU defense would bottle up teams like Bama at full strength (if Bama needed to score), Clemson, Oklahoma, Texas (the way they played last night), Ohio State, etc.