It's all mental with McLemore, and he himself said it multiple times in the post-game interview. McLemore has always been a hardworker. Coming into the NBA as just a kid, it impacts everyone differently. He had an extremely rough upbringing, and there were a lot of people knocking on him for his maturity. Is his head going to be in the right places? Is his head at the right places? How fast can he mature as a person on and off the court? Does he have the mentality to be anything more than a spot-up shooter? Does he have the confidence and capacity to assert himself as more than a 3rd option?
Being drafted by an unsteady Kings team didn't help his development very much. 4 different headcoaches in each of his 4 years here. Constant internal problems with the FO. Major problems between coaches and players. It's not hard to see where problems could've gone wrong with McLemore.
I'm not sure if he can sustain his high level of play, but it's always been mental and confidence. He just needs to finally put it all together. As it stands right now, he has all of the physical tools and skills to be a starting SG. Contrary to popular belief, SGs don't need to have a ball handling to dominate. Look at Klay, Beal, Gordon, Reddick, Matthews, and Hood. These are all guys who play mostly off-ball. It's a lot easier said than done. I really hope he can breakout before his contract ends. I don't know if he he has a long-term future here, but I do know that he has a place in the league.