The problem in this scenario is that no one thought Leonard would be as good as he has become. So any players who are considered to be high upside players today can't be considered for this exercise.
Leonard's comp was Mbouh a Moute or Gerald Wallace on nbadraft.net (not a great site, but we'll go with this for now). His strengths were evident, but his weaknesses were that he didn't have a move with which to score consistently, he didn't have a consistent jumpshot, and he gambled on defense.
For this exercise, the guys I have an eye on are Troy Brown, Bonga, or Baites-Diop. For a different position, Porter or Wiley might be guys to consider.
Fun exercise. Good thoughts. It'd be sweet to get a big to complete the young core.