My thoughts on this:
1. Michigan was really good in the Cooper years! Cooper's first two OSU teams, which had nowhere near Michigan's talent level, played them hard. But it was no surprise that they lost.
2. After that, the talent gap shrank and there were certainly plenty of years where the Buckeyes were actually better, but I think at a certain point our issues beating them got into our heads (as I think it's now started to do on the other side). The 1995 result can only be explained by a massive teamwide choke.
3. Our bowl matchups were likewise pretty brutal. It's never easy for the Big Ten to beat a really good SEC team in a Florida bowl, and that was usually the situation we were in in the 1990s. And for some reason, we almost always struggled on offense in our bowl appearances under Cooper, "highlighted" by the brutal loss to Air Force in 1990.