I think you more or less proved them right.
What I mean is this: calling a draft "weak" could mean that it's "bad," i.e. that it doesn't have many good players in it. Alternatively, it could mean that the draft doesn't have very many strong prospects.
The former is about outcomes -- in five years, how many "good" players will have been selected in this draft?
The latter is about the perspective of draft evaluators looking at the draft for the purposes of making a decision on draft day.
Who should go 5th? Who should go 10th? Who should go 15th? Who should go 31st? In a strong draft, it might be easy to answer those questions. In a weak one, maybe you find yourself wanting to throw up your hands. Too many guys with major flaws, questionable strengths, slim scouting reports ... a wide range of possible outcomes.
2009 was considered a "weak" draft too, as I recall. When you look at it now, it was kind of epic.
But the fact that a bunch of guys selected in the 20-40 range in the 2011 draft turned into really good players is small consolation to teams that were picking in the top 10, trying to make a pivotal choice for their franchise, only to come away with Jan Vesely or Bismack Biyombo.
In short, pointing out that many of the best players in a given draft were taken in the second half of the first round or later is pretty much proving that it was a "weak" draft for the purposes of the people making decisions on draft day.
"You have a better chance of getting somebody good taking a shot in the dark in the second round than making an agonized decision in the top 10" is not exactly a ringing endorsement of a draft class.