You might be right, but the problem with evaluating players so early is that when they finally blossom, it's then done in Europe.
And this is why there would be four or five Euroleague teams which, in an NBA conference, would have a level higher than play-in.
Between teams full of young people to develop or to tank, poorly constructed aging teams, poorly balanced teams with two overpaid stars (often injured) and role players, some of these teams in the NBA are not really compe ive.
There would be around fifty players playing in Europe who could strengthen teams relegated outside the play-in. Problem is, these NBA teams still have to develop their own talents and the big players in Europe (including a good half of American players) cannot contractually come.
Not only can GMs make mistakes on players, whether or not they wait until they turn 25, but this also considerably weakens the level of the league then made up of big teams and teams worthy of a development league.
This is also probably the consequences of the draft. It might be time to consider moving to a single-round draft, requiring an age of at least 22, and making it easier to buy out Euroleague player contracts.
Seeing three teams out of 30 that are “under reconstruction” is still acceptable. When you have a quarter of the teams that are in a process of either development, reconstruction, or in-between, it is already more problematic for the spectacle that the league supposed to be the best in the world offers to the public.