There are many gradations of wide open. Any meaningful evaluation of a 3 point defense necessarily needs to account for proximity beyond the simplistic divisions of 1)"wide open" and 2) "contested".
For a college level three point shooter the difference between wide open, open, barely contested, and lightly contested are about the same in terms of difficulty. Dakich mentions this every game--a lightly contested shot is like a "sight on a gun".
Per Kenpom's theory, Michigan has a decent 3 point defense amongst big ten teams.
I love Kenpom. I won quite a few brackets challenges by studying his site 15 years ago for way too many hours.... HIs expressed opinions on 3 point defense is fun conversation starter but he oversimplifies the issues involved. There are a lot of factors.... It is a mistake to look at a team that has a low number of 3 pointers against And to assume, conclude, or even be confident that it means that particular team is good at defending the three.