it's really hard to tell whose shooting is going to improve once they get to the league and who won't improve at all and who will regress. the mechanics is one thing to look at, but most people just have solid mechanics - nothing special, not terrible not Hawkins beautiful. and it isn't just about mechanics, it's work ethic, are they in the gym getting shots up, are they put in positions to succeed on their nba team, does the coach have patience with them, do they get the green light, nba spacing works better for some than others, etc, etc. so many factors, many you just can't see and have no clue of. draft good, skilled players, athletes, guys with length for their position, and hope for the best. kawhi is a great example - the spurs drafted a dude who was a really good college player, a guy who could defend, rebound, who played hard, had positional size. his stroke was okay, certainly nothing special, but i imagine they though they could work with it. worst case you get an energy guy who can defend multiple positions - best case, you get who kawhi became.