To be fair, he got a bit of a pass last year because the offense was so good. We've had so many fewer possessions on defense, it's hard to give our defense a pass when they finally have to deal with what a normal defense handles.
I don't think the offense has been as bad as you make it out to be. We've lost games scoring 22, 20, 31, 24, 28, and 21. It's not like we've lost a game despite holding a team to under 100 yards rushing or under 20 points. Call it "morale," or anything else you want, but the defense was bad last year and was bailed out by a pretty good offense (see, e.g., giving up 31 points to duke, 48 to unc, 28 to pitt, 23 to NC St, 37 to fsu, and 34 to miss st). We just don't have the offense this year to mask how bad our D really is.
The #33 defense in the country in terms of scoring (Duke), gives up 21.7 ppg. If we could hold the other team to the low 20s we'd have at least 2, maybe 3, more wins. Not counting that a number of statistics show the defense has gotten worse, not better.
That said, the biggest turnaround has been on turnover margins. We aren't in the top 50 in turnovers forced. Combine that with the number of big plays we've given up, and our generally mediocre at best run defense, and that's what is costing us games - not necessarily the offense. If we had a top 25 defense this year, as many were hoping, we'd have a lot more wins.