Iowa also didnt pay the bottom 2 of the list, MSU and Rutgers.
ISU got to play the bottom 3 offenses in both leagues combined last season.
Let me break this down for you.
Iowa schedule vs ISU schedule
PSU avg 33.8 OU avg 48.4 for a difference of 14.6 to ISU
PU avg 30.5 WVU avg 39.2 for a difference of 8.7 to ISU
UW avg 29.7 OSU avg 36.8 for a difference of 7.1 to ISU
MN avg 28.9 WSU avg 35.8 for a difference of 6.9 to ISU
UN avg 28.6 TTU avg 33.7 for a difference of 5.1 to ISU
MD avg 28.5 UT avg 31.1 for a difference of 2.6 to ISU
ISU avg 26.8 UI avg 30.6 for a difference of 3.8 to ISU
IU avg 26.4 BU avg 27.4 for a difference of 1 to ISU
MISS ST avg 25.7 KU avg 22.1 for a difference of 1.8 to Iowa
UI avg 25.3 KSU avg 22.1 for a difference of 3.2 to Iowa
NW avg 24.2 TCU avg 20.9 for a difference of 3.3 to Iowa
Now, I guess your argument would be, "Well the reason for this disparity is that the Big XII doesn't play defense". And then you can look at the out of conference games and see that the Big XII held most of their opponents under their season averages. Most rational human beings say it's a bit of both. HIgher octane offenses exist in the Big XII and strong defenses are in the Big 10. But the disparity doesn't quite result in Iowa being a juggernaut defensively.