Kawhi could shoot tbh. Watching his combine footage, you could see he had the touch, feeling and coordination to become a shooter. It was a question of putting on the work and repe ions, maybe twisiting a couple things. Sidy is too raw in that domain to ever become a reliable shooter.
It's not that simple to teach how to shoot, and not automatic, specially with big dudes. The player must have it in him. You can work all you want, if a player don't have what it takes he'll never be a shooter in the NBA.