Not really following that logic. Kugel and Harris are playing plenty and not really helping the defensive situation. And not sure Clary was known as a defender though he would have likely helped us offensively as a PG.
I was really speaking to the comments above mine about overall improvement and "why aren't we as good as we thought we would be"...
I see that you are trying to answer the OP, which focused on 3-pt defense. Sorry, I wasn't trying to answer that question. My answer to that would revolve around guys this year being offensive-minded players, who save their energy for the other side of the court. Unlike DJ, who by the end of his career here had transformed into an elite defense-first player. He was dedicated to popping out hard on 3-pt shooters, even if he was forced to double in the post on the same play. That takes maximum effort and willingness to play your asss off on that end... which we don't always have this year.
Shawn Jones goes all out on D. RJ gives great effort but not all the time. Cam does it (most of the time). Murph is learning to play pretty good defense. Harris gives good effort most of the time too, but not 100%. Plus he's not as long as DJ so they shoot over him as he recovers.