You forgot Cincinnati. Know who else hasn’t beaten a top-25 team? Number FIFTEEN Iowa. The difference is that Notre Dame hasn’t lost to weaklings like Wisconsin and Purdue.
Of course, if Iowa beats Michigan, I won’t be able to deny that Iowa will have beaten Michigan. Just like Michigan State has already done. And Michigan State will have objectively beaten tougher opponents than Iowa has beaten, and loss only to tougher opponents than Iowa has lost to. Heck, even if Iowa beats Michigan, Michigan will STILL have a better resumé than Iowa (not that I expect whatever powers that be would give Michigan a nod, since they invest the conference title with too much significance to do that).
If Iowa wins, they would be the only Big 10 team contending.
The ALA win over Auburn may prove to be the death of IA, ND. ORE