4 great seasons out of 19 is better than the norm for Iowa football, going back to 1889. Hayden's tenure was very similar; several good seasons but only a few great ones.
I think the fundamental problem with you is your expectation level. You want us to compete toe to toe with Penn State, Ohio State and Michigan every year. I get it, but it is not going to happen. Your sample size is almost 40 years now: The Fry and Ferentz era.
Here were the great seasons during that era, in my very humble opinion:
1981 - Big Ten Title
1985 - Big Ten Title
1990 - Big Ten Title
1991 - 10-1-1 Big Ten Runner-up
2002 - Big Ten Title; Orange Bowl
2004 - Big Ten Title
2009 - Big Ten Runner-up /Orange Bowl win
2015 - Big Ten West Title - Big Ten Runnerup - Rose Bowl
There were a lot of good years, but only 8 great ones, in my opinion.
It is impossible for Iowa to be great year after year. It isn't going to happen, for lots of reasons.