I have a different take on draft evaluation. Going back to the draft odds chart (link here -
http://nyloncalculus.com/2016/06/17/freelance-friday-expected-value-in-the-nba-draft/ - not posting it because it's already been posted a few times elsewhere), you will see that a team that has pick #6 or below has less than 10% of drafting an All-NBA team player, and once a team is out of the lottery, team's chance of picking an All-NBA player is almost 0%.
To me, that means teams do overall a really good job of evaluating talent, particularly difference makers. (Plus conventional wisdom says that the NBA is the easiest league to evaluate star players, even from a young age.) That's obviously not to say that every young player ID'd as a potential star is going to be a star, but that does mean that there aren't a lot of guys - particularly those in the US system - who are going to come out of nowhere and become all-NBA.
And eventually, we'll be on European prospects like we are on US prospects.
I think the last few drafts have been evaluated pretty well in terms of who might become all-NBA. Sure Ingram might be a bust and there is probably a late bloomer who emerges from outside the lottery to become a star, but for the majority of the picks, people were probably pretty accurate in gauging their range.
As for next year, people are saying that if Fultz came out next year, he'd be lucky to be the 4th pick in the draft - that Ayton (7'0", 243), Porter (6'10", 214), and Doncic (6'8", 185) are clearly ahead of him - and that there may be others who could jump up into that conversation. One thing for sure - there is a ton more size at the top next year than this year.