regarding the bold...I wonder how much the "grooming" helps. Khyri Thomas left a year early, got drafted in the 2nd round and has either been D-league or riding Detroit's bench all year. I have to wonder how much development is actually going on with guys that don't actually play. How much do NBA teams really "practice"? Weigh that against actually PLAYING 30 minutes a game for 30-35 games (with a coach that knows what it takes).
That said, Khyri is making $850k for 2 years guaranteed so there's that.
It depends on the player and situation. Danny Green did this process after his junior year at UNC. Got some input, came back to school and still didn't make a team. Pop is friends with Roy Williams and he told Roy what Green needed to work on. He spent a few years in the D league until the Spurs signed him.
If a guy is willing to take constructive criticism and work at improving, it does happen.