I think if you are higher than the 4th pick in the draft it can be very valuable to start looking at 19 year olds. 19 year olds can be very good, as you said, a lot of people just do not like training them because they missed their fastest year of training and generally people like to get a new round of trainees every 4-5 seasons, and it is easier to buy a cheap 18 year old on the TL than train a 19 year old to be where you want them, when you want to move on to your next group of trainees.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs