I think length is least important at the 1. Motor, physicality, foot speed, smart rotations, explosiveness are far more important defensively, as I see it (I have little/no data to support this). Larkin is better than pretty much every other point guard in this draft by those measures. Is length the only knock against the guy, or is there some other reason people don't like him? I haven't seen him play that much, admittedly, but have the detractors?
Qman mentioned turnovers and Miami's talent (a team ranked 4th in the ACC in the preseason by ACC coaches...), which is a start, I guess. Again, does anyone who's actually seen him play have reasons not to like him other than length?