Exactly how high do you think it is?
With his length and athleticism, he can be a plus defender in the NBA, and being an above-average NBA 3-point shooter is within reason. I don't think he'll ever be a starter on a decent NBA team, but I could see him being a rotation player who comes off the bench for 15-20 minutes a night to defend 1s and 2s and hit open threes. To me, that's his ceiling rather than what I expect on average.
The problem is that in any given draft you can make a similar argument (i.e. he has NBA length/athleticism and maybe NBA skill 'X') for a number of prospects in that late first round to second round range. For those guys on the fringes, whether or not they stick (and how well they do if they stick) is so heavily dependent on the teams that draft them, in terms of a team's willingness and ability to develop them.
Getting waived by the Cavs may have been the best thing to ever happen to Danny Green. DeMarre Carroll was cut by the Rockets and the Nuggets, and he may end up making double what Green is making right now. Even if a player is good enough, it takes a bit of a luck to land in a situation in which he can prove it.
