As usual, people are going overboard with this.
Two things can be equally true:
1) This season's Keyonte is a much improved, very useful offensive player. His increased impact on that side of the ball is particularly evident on the Jazz, as Lauri used to be only one capable of providing consistent volume scoring, night in night out. That isn't the case anymore. Key deserves his flowers for getting stronger and better.
2) Keyonte's awful defense is seriously holding him back. It's not "mid", it's not "meh", it's not "he could be better I guess". He's hurting the team in a major way. Dunksandthrees.com says Key has the 2nd worst defensive impact in the entire NBA. Read that again. He's deep, deep in the red. (As an aside: Collier is almost as bad.) It wouldn't be much of an exaggeration to say that for all intents and purposes, Keyonte doesn't play defense.
The current Key is a true Jekyll-and-Hyde guy. The gap between his offensive impact (much better than average) and defensive impact (bottom of the barrel) is absolutely massive. People like to point to guys like Brunson as similar cases, but while Brunson is a minus defender, his offensive impact is legit superstar level. There's no comparison.
Overall, this season's Keyonte is an average NBA player. Fans like to ignore defense when someone starts putting the ball in the basket, but defense matters. For instance, a widely used catch-all impact metric like EPM ranks him at 203 in the league. Lauri is at 16. It's wild that Key is that low on a team where his offensive impact has been massive this season.
So no, Keyonte isn't even close to being a star. He's such a bad defender that even getting to an average level will be a massive task for him. There's no guarantee he'll ever get there.