Johnson's basic flaw is his lack of BB IQ. It shows up in both the defensive and offensive sides to his game.
Offense: He is still subject at times to making mindless bull rushes into the lane where he lowers his head and decides to go one on one without any sense of what his teammates are doing. Granted this has improved somewhat since his rookie year, but after four seasons, some as a starter? Puhleeze. I don't think he was ever a natural shooter coming into the league but worked on his shooting with pretty good improvement. But, as was shown last season, this aspect of his game is not written in stone. He didn't improve further, but actually seemed to regress a little in his percentages. Natural shooters don't let extra attention from defenses or "carrying the load" affect them that much. His shot selection isn't what we woulld like to see. Not a good or natural assist maker because he doesn't have the court vision.
Defense: IF it takes the addition of a generational talent like Wemby to give him the opportunity to become an AVERAGE defender in the league, you must agree that there is a problem here. Partially it might be that his physical speed and athleticism isn't up to par against the compe ion he faces night after night. OK. So if he gets beat, we hope that someone else will do his job much of the time. But if you combine that speed and athleticism problem with low BB IQ (which I believe is where he's stuck) then you can see the problem. After all, we've seen plenty of players with some lack of speed or athleticism make up for it by using superior BB IQ. They learn the nuances of the game and study the films to learn the quirks and moves of their opponents. Sometimes a player can make a subtle adjustment in his alignment to protect against a player who can't go left. Other times you give a player who can't hit the three some extra room. Knowing when to rotate on defense to help out. Positioning for rebounds. The nuances are endless and players should be able to make those fine tuning adjustments after 4 years in the league. I don't see that happening with KJ. He is what he is. Ceiling. Full stop.
He's already at the point where other players already are at his heels in terms of their potential to take away his starting job as the lineups are adjusted because of the addition of Wemby. If I were a coach, I would never trust the idea of removing a starter to a lesser role on the bench. Few players can accept that demotion psychologically and thrive. This is a hard business. We let Derrick White go because he no longer fit our needs. Time to do the same for KJ.