Overall, RJ is showing improvement as a player the key areas we hoped he'd improve - his shooting (FG/FT/3pt percentages are all up) and defense.
I looked at RJ's game log and did some math. RJ Barrett has been on an incredible tear from 3pt range for the past 24 games of the season.
Games 1-11: (he ended game #11 0/5 from 3pt; 1/2 from the line)
3pt%: 18% (9/50)
FT%: 68.6% (35/51)
Games 12-35:
3pt%: 46.4% (32/69)
FT%: 75% (63/84)
Given that he's been doing it for over 2/3 of the season, I think we can fairly safely say that he is indeed a better shooter than he was as a rookie. His 3pt% over this 24 game stretch is above Steve Kerr's NBA career best .454 from 3pt range (Kerr averaged 1.8 3pt attempts/game over his career). How's he doing it? He's taking good shots - Most of his 3pt shots are in the flow and with ample room (much like Kerr!).
I think the main area for improvement for RJ is his finishing near the basket. He usually takes a couple of duds in his drives to the basket each game - he seems to expect to draw contact but the defenders keep their distance, leaving him up in the air, with no choice but to throw it up and pray. One thing he'll surely work on is reading these situations better (defenders retreating to guard the layup) and have a better plan. Maybe he's jumping a step early... or maybe he needs to stop on a dime and set himself up for a short 5-10 fadeaway jumper instead.
One other thing for him to work on over his career is establish a post up game. He has the frame/strength to do it - but a team that features Randle in the post will have to make a concerted effort to develop this skillset in RJ.
Lebron anecdote: For the first 8 years of his career, Lebron was primarily a face-up player. Is 6 out of his first 8 years in the league, Lebron's FG% was below 50%. After hooking up with Hakeem for some summer workouts in 2011 at age ~25+, he's continued by shooting over 50% for 8 of the next 10 seasons (including this season).