What did KK do? Glad you asked. Although his average with Minny was an underwhelming 43.5%, he went 50% on FG's with the Nugs, good for maintaining a respectable career 48%+ FG overall. THAT's what he did with the time he was given--which totals over four seasons what most bigs need in one season to progress. In KoKo's case, we're talking the equivalent of less than 15 minutes per 80 games, or half as many minutes in four seasons than Greg Ostertag--nary a big-man bastion of discipline or even skill--had in his first two seasons.
Was it because of the Big O's statistical superiority? No .... He averaged around 50% FGs in his first two years, only mildly higher than KK's 48%. What about rebounds--a key benchmark for big men? Well, Ostertag averaged right around 9 RBs per 30 minutes vs. 8 RBP30 for KoKo.
Sorry, Glassy. Kosta is only one of a litany of centers who (with a minimal amount of development) could make / have made a positive contribution at the much-understaffed 5 spot on the Jazz if they had only got the requisite on-court playing time. (KoKo only trailed Ostertag mildly in production after only half the minutes in his career. It's reasonable to imagine that he could close that gap with similar PT.) But instead of efforting to find the minutes for these developing bigs, Sloan (and possibly his successor) preferred to usually go with his prized Matador and Torero, Boozer and Okur (plus a usually good choice in Millsap, but not requiring so many minutes for the minimum development time that he needed), more often than not, even when it wouldn't have change the outcome of the game (except possibly getting aroudn to it in the last 3 to 5 minutes of the game), and even when such backup bigdoes take his precious scraps of minutes and does something good with them--but often didn't get rewarded for it with more modest regular minutes.
Yes, it's true that Kosta was streaky. But he was also young. And he usually worked hard. And he was making progress before Sloan starved his court time to barely nil. BTW, you could replace Kosta's name with that Ukrainian 7-footer--his name escapes me /sarcasm/--who was a diffference in turning the momentum in multiple games over his few seasons with the Jazz, even though his shot was also erratic. Oh, and there's that Brazilian backup big who neutralized Tim Duncan in a game or two in the playoffs despite having T-Rex arms and a sometimes uncontrollable strength. Was this a highly damaging pattern over multiple years during the Sloan regime? You bet. Was it even restricted to the 5 spot? No way. Exhibit 1 (really Exhibit 2 given that he errantly played SG a lot): Derek "40% FG all season, yet we remember you when you flied back into town and helped the Jazz win a solitary game after stiffing the Moran Eye Center on your daughter's care" Fisher.