Well, you know (or, at least won't acknowledge) Iowa's defense has never been able to handle a good spread offense during the KF era. The best Iowa's defense could do against any good spread offense was to delay the inevitable long enough for a turnover or a stop on fourth down.
This 2016 version of Iowa's defense also can't stop any playmakers in a spread offense. Side note: Did you watch any of the LSU vs. Alabama game? LSU has about as, in your words, futile an offense as Iowa's yet kept the game close the entire game with great defense. Iowa doesn't, scratch that, has never had a great defense against playmakers in spread offenses under KF.
To your point of Iowa's defense being on the field for 72 plays: Iowa's defensive scheme is designed to be on the field for long stretches of the game. That's the concept of Iowa's defense. Bend and bend and bend but don't break. Can you see where Iowa's defense is regularly on the field for extended amounts of time because the defense scheme calls for it?? What has the defense done to change schemes to change this alarming trend in Iowa's defense? Bend and bend and bend but don't break is fine, if 20th century. Bend and break and break and break quickly is not.
If you understand Iowa's defensive scheme is to keep the defense on the field for extended minutes in a game, you understand this also limits the amount of minutes Iowa's offense gets and also why at the end of games Iowa's defense is always so pooped.