I've watched a couple ND games this year: aTm, part of NIU, Purdue, some of GT, Navy, and USC.
Similarly, I have watched some IU games this year: Michigan, tOSU, and some of Purdue.
I cannot really tell if either of these teams is any good. ND's SOS is 64. IU's is 74.
Fwiw, IU got whipped by tOSU, but tOSU also had TD drives with short fields due to IU's inferior special teams play.
That said, IU has a statistically good rush defense for a reason: they played teams with crappy run offenses. Given each team has at least 12 games under its belt, rush offense rankings have some meaning. The best running team IU played was tOSU, ranked 52. 6 of their opponents were not in the top-100. 3 more were in the 90s. Early in the year, you could say "because of their defense" - now, it is because they played crappy running teams.
What I find interesting is that UND is only -6.5. Some predictors - based on computer models - would have them as -8 on a neutral site, placing them at -11 since it is a home game. Perhaps the cold weather is causing the derate, or lack of confidence in their ability to blow someone out, or heavy money on IU.
I see this as an entertaining game, and will be cheering for IU. I hope they win by 10+