Looking at the data:
- I took 281 college players drafted from 2011 to 2020.
- I filtered by players that played a minimum of 164 games in the NBA.
I compared their college 3-pt shooting percentage to their NBA 3-pt shooting percentage.
On average, players only improve their shooting percentage by
0.7% (if they shot 35.0% in college, they shot 35.7% in the NBA).
Also, I looked at their FT% to see if that was a good indicator if they could more easily 'learn' to be a good 3-pt shooter. I found no correlation -
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My conclusion: Becoming a good NBA 3-point shooter is not easily learned. What the player is in college is probably what the player will be in the NBA. Sample size is of course a factor. Free-throw shooting is not a good indicator if a player can more easily learn to be a good NBA 3 pt shooter.