Without searching any archives, I recall Iowa always having trouble defending the 3, going all the way back throughout the Davis era.
Not so sure it's "Iowa", or even "this team" but more the inherent by-product of playing so much zone defense. It tends to "force" the other team to take more outside shots.
As I said in another thread, it's not so much playing zone that's the problem, it's that "this team" is just not very good at executing zone defense. I've seen it asked, "Why stay in the zone when they are getting pummeled with the 3?" I see it as a coaching strategy to play the lesser of 2 evils -- although "this team" is not very good at zone defense, Fran sees that they simply don't have the depth (energy) or athleticism to primarily play man-2-man. (You think Cole and Brommer get in foul trouble now, it would be even worse going man. Not to mention that the guards / wings would repeatedly get beat off the dribble.)
Fran opts (hopes) to force the opponent to beat them from the outside. As someone said above, they'd gladly take an opponent shooting 30 - 3's and making 10 over one taking 10 and making 5. It's all about forcing the opponent to take a lower % shot.
The problem with "this team" is, because they execute zone defense so poorly (poor court awareness of cutters and ball movement; way too much over-helping and leaving their zone) the opponent gets too many clean looks from the outside. At this level, there isn't much difference to a shooter between an uncontested 15 footer or an uncontested 22 footer, except an additional point.
Right now, Iowa's "best" defense is hoping the other team has an off-shooting night. That's not as likely as long as they continue to get such open shots, regardless of whether the Hawks are in zone or man.