There's nothing "generalized" about the top 6-7 slots constantly generating much better players overall. There will always be dumb FO's who pick the Greg Oden's of the draft. But if PATFO are really as good at drafting as people claim, then they should damn near have a lock on a top-tier player if they ever pick that high. (No, I didn't say franchise player, although their chances are much better high than low.)
It might help if some of you watched any college ball. Cole Anthony (son of Greg Anthony) is going to be an NBA baller. He had knee surgery, but I'm still pretty confident he'll still declare this year. He may fall a few slots, but not far enough for the Spurs to get him at 16 or whatever. Anthony Davis will be logging NBA minutes next season. Lamelo Ball too, even though he was playing in Australia, not NCAA, and now he's hurt. (People here will bash him because of the family.)
I've been a Maccabi fan since I lived and worked over there for a while. They have a kid named Deni Avdija who has a shot at being a good NBA player. If he declares this year he may be within the Spurs' grasp. I thought Aaron Nesmith might be a Spurs fit in that 16-17 range, until he got injured. But guys like that are dart-throws. It's a totally different thing picking at 7 or higher, in any draft.
It's the density of good players that make the statistics.