You can't possibly know this to be true. You can believe it, you can assume it, and you can say it. But it's nothing but your opinion.
Had he put on 10-15 pounds, returned to show more aggression, more consistency, and better rebounding, he certainly could have improved into a first rounder. He could have easily averaged 20 and 8 on this team and shown the ability to be a consistent scoring threat.
It's possible that would not have been enough to get him into the first round, were it not, Australia, Israel, and Europe will always be viable options. However, it's not unimaginable for a senior to play himself into the first round (see: Napier, Shabazz).
If you can't understand the HUGE difference between being pick #30, and pick #31 (literally a few million guaranteed dollars) then you'll never get the point @Jerry1714 is making.
Yes but you're arguing hindsight knowing where he was actually drafted. The argument has to be:
1) Should I declare for the draft? I'm currently projected mid-20's in mocks, am coming off a national championship and clutch tournament where I think I just played myself into the first round, and I am already old (22). Best case scenario: Workout my way into the lottery. Worst case scenario: Bad workouts, 2nd round pick.
2) Do I try to return to school to get a better draft slot? I'm probably not going to get the tournament run exposure next year I just did and I will be really old for NBA draft picks (23). I may show more holes in my game and there's a decent chance I don't improve that radically or continue to show the inconsistency I've shown my whole career, but I may also dominate college hoops and become an All-American.
Best case scenario: Dominate college hoops, probably end up a mid first rounder (23-year old lottery picks just don't happen). Worst case scenario: Game is exposed, don't even get drafted.