for a numbers-based perspective, the UNC defense finished the season ranked 100th in defensive FEI. That's worse than Gene Chizik's defense last year, which finished 74th.
Fremeau helpfully maintains a list of teams' weekly progressions, and here's UNC's.
There were basically 3 good weeks: Week 9 against UVA (gain from 101 to 82), 10 against Syracuse (gain from 82 to 68), and 11 against Stanford (hold at 68). The efficiency numbers say that the performances against Wake, Duke, and State were all in line with the early season performances against Clemson/TCU/UCF, just against worse offenses.