That 2002 team was loaded with NFL draftee quality defensive talent, and quite frankly, had decent players on offense as well. This was a veteran defense that worked well together, and essentially coached themselves. They were able to do a fine job in 2002 despite Kent Baer's idiotic constant "stack the box and let the DB's fend for themselves," even on 3rd down.
That 2002 team was also the luckiest ND team when it came to opportunities.
The offense was terrible. Running a West Coast offense with a quarterback who couldn't throw an accurate short ball was a display of sheer stupidity, but of course, Bill Diedrick refused to modify things, and WIllingham foolishly agreed to leave him alone.
Then Willingham became the laziest recruiter of all time. There were plenty of 4 and 5 star players who would have loved to come to ND, but Willingham didn't reach out to them. Instead, he simply waited on his lazy ass, and accepted whoever decided to show up in 2003 and 2004, leading to the two worst recruiting classes of all time at ND (2004 and 2005 classes). That 2005 class would have been even worse if Charlie Weis didn't manage to snag a few decent players at the end (Duncan, Turkovich, and a couple others).
Clay Helton is at least a competent coach, and works hard to bring in good talent. JT Daniels is going to be fine once he's had an off-season of strength and conditioning, and there's a lot of talent coming up through the ranks, especially St. Brown.