Funny thing about basketball, is that NCAA bigs don't have to be great. Just good enough to contribute to making their team better and of course winning. To me a big that rebounds and defends at a high level is Div 1 ready. The refinements (i.e. assists, scoring, ball handling, etc.) will come with more coaching, practice and conditioning. Many schools aren't capable to help them with refinements, but a school with an experienced coach ( ) will get them NBA ready.
A lot of HS bigs only look at playing time and exposure and mistakenly don't value refinements (which is really improvements) when selecting. Understandably, they think they're better than they really are, because of high school domination.
No finer example than one Jake Voskuhl. Never scored twenty points in a game in high school, college or the NBA but had a long career and made lots of money due to his fundamentals.