One of many problems I have with Kelly is I don't think he is capable of going 14 straight games (nor 13 before the playoffs) without personally making in game errors that cause the team to lose at least one game per season. Thus, he is incapable of winning a title at ND becuase I do agree with you that to win a title at ND we have to go undefeated.
I think Stoops and Richt are capable of going some seasons without the in game mental errors Kelly makes that guarantee we lose at least one game per season. Thus, they at least theoretically have a chance -- whereas I think Kelly has no chance at all.
I then think they both have shown an ability to field a good defense and an offense that can run the football. I actually prefer Richt more, because his SEC background gives him a power football -- run first -- mentality that I personally believe is what ND has to have at it's core to be capable of going undefeated. We cannot scheme our way to 14 wins per year. We have to be able to impose our will and have to be able to run or pass as necessary to deal with the variety of teams we play each year.