Kessler is literally the tall guy at pick up who only wants to shoot 3's. He should listen to the staff. Wanting to shoot 3's instead of being inside the paint is not the greatest look for him given his struggles. I'm not sure you can really teach/develop a mentality though. My guess is that he fluctuates up and down between his year 1&2 level depending on his mental state.
Shooting 3's has more potential to make him worse than better imo.
During offseason workouts there is plenty of time to do both. Some of you are acting like he can only do one thing at a time. There is no reason that he should be getting up at least 200 3's a day during his workouts as well as a ton of mid range and post of shots. The guy is working with a couple rebounders so you can get up a bunch of shots really quick.