Well, besides the obvious issues of recruiting at Iowa versus many other places whose head coaches go from college-to-pros(egs. Carroll, and Saban).
The strength of KF is as a teacher of the game not in recruiting(obviously something he won't have to do in the NFL).
Iowa has the 8th most players in the NFL of any program inspite of recruiting at around the 40th best level. Obviously, his program makes players NFL ready at a rate much higher than at most programs. Arguably, Iowa is the best in the country at developing NFL players.
His experience at the NFL level came as a coach under the best coach in the league, and his son is a member of that coaches staff(a indirect compliment of KF).
He runs his team in the NFL model. So, everything from the language of the plays, to film breakdown, to the offensive and defensive schemes are out of the pro model.
So, while there are coaches who have more innovative offensive minds and have better records at elite programs. KF's talents are principally as a teacher of the game and as an administrator of the program. In some ways KF's greatest coaching strengths are more tailored for the pros than college ball.
I could see why KC would be interested in Ferentz. He's probably more impressive to Pioli than an outside observer simply because he knows Ferentz's mind and has seen his "product"(players) up close.