OK, BGIF. You wanted the statistics. Here they are and they tell the whole story. This is based on Willingham's last 18 games and Weis' first 18 games. These statistics are courtesey of UHND.
Win/Loss Willingham/Baer 9-9
Weis/Minter 14-4
Total Defense Willingham/Baer 6,498 yds (361.0 ypg)
Weis/Minter 6,849 yds (380.5 ypg)
Scoring Defense Willingham/Baer 422 points (23.4 ppg)
Weis/Minter 436 points (24.2ppg)
Minter's stats are worse in all cases. Also, as we all remember, Willingham's offense was terrible, which caused the defense to be on the field for long periods of time. On the other hand, in most cases, Weis' offense controls the time of possession which means the Minter defense is on the field less. That makes the above numbers all the more damning. The won/loss record is due to the Weis offense scoring more than the Willingham offense did.
Charlie took the same players Willingham had and turned the offense completely around. Minter took the same players Willingham had and did nothing with them, NO IMPROVEMENT. In fact, based on the above numbers, SLIGHTLY WORSE. It all points to coaching and/or scheme.
Now tell me we don't need a change!