There's 3 eras in Kelly's time at ND:
1. Buildup to NC game
2. Fallout
3. Post 4 win season Kelly
IMHO only version #3 can compete with Lou Holtz. Lou had to do a different kind of rebuild as well when he got here and had more success against TOP (USC, Miami, etc) programs. Moreover ND was closest thing to modern Alabama during that time.
Lou was great out of the gate and fell off towards to end, but still got 2 National Championships (I count '93, I don't care who doesn't and could have had 3). Kelly is still figuring it out and is dominating COVID football. He could have been justifiably fired in the middle of his time here whereas Lou couldn't have been.