I think his point is more that Ainge quite simply hasn't been winning since Rondo was selected when looking at picks in that range. It would be one thing if he had those 7 awful picks but also had 7 of the better picks or even just 1 of the super-elite All NBA type players. But Ainge doesn't have those. He is missing or getting a single. His best selection was Avery Bradley, who is a fine player and very good value for his draft spot, but he isn't moving the needle much.
I think you have a different definition of "not winning".
Rondo was one of the greatest value picks of all time so isn't really a fair threshold to hold every pick since against.
But when talking about picks 'in that range', he's picked Avery, Sully, Fab, and Zizic all within 2 slots of Rondo's pick. Fab is a bust and the jury is still out on Zizic but Rondo, Avery and Sully were all clearly 'wins' in that range. I'd call that hitting at least 3 of 5, including a home run, a double and a single. And maybe count Zizic as a walk.
What percentage of players at that range ever become 'home runs'? What is your actual threshold by which you are judging?
If we use the 82games.com study of drafts from 1989-2008, only about 5% of players picked in the 19-23 range are going to be a 'star' and almost 60% are going to be no better than deep bench players.
The percentages drop off to abysmal quickly after that as you go deeper in the draft. By the time you start the 2nd round, you should expect 70-80% of all players picked to be no better than deep bench players. By the time you get to the middle of the 2nd round, forget it.
I get the feeling from reading comments that folks just don't really just how stacked the odds are against most of these players being even average NBA players, let alone 'home runs'.