Where do you get these statistics from?
Well, just out of curiosity I went and looked at the rates of different picks being stars. For simplicity I took any player that had made at least one all-star game and/or one all-NBA team (1st, 2nd or 3rd). So this includes guys who made a single all-star team alongside HOF'ers. But at the very least it separates out relative busts from what I would consider a successful pick.
I started in 2012 which was the first year that any player taken 1, 2, 5 or 10 made an all-star or all-NBA team. From the 2013 draft Giannis was an all-star and he and Gobert were 2nd team all-NBA but they weren't taken in the slots being discussed. Anyway, I went back 25 years (back through 1988) and here's how often each slot reached an all-star or all-NBA level sometime in their careers:
76% of #1 picks
40% of #2 picks
40% of #5 picks
28% of #10 picks
Of the six #1 picks that didn't make an all-star or all-NBA team, 4 out 6 years, the #2 pick did. Durant, Aldridge, Tyson Chandler and Antonio McDyess. Only once did all four make the cut - in 1994 with Robinson, Kidd, Juwan Howard and Eddie Jones. Grant Hill went #3.
So this would seem to indicate that the #1 pick is hugely valuable but that the #2 pick is on average the same as the #5 pick.
But of course what that really means is that teams picking at #2 have missed more often than they should have. It's worth noting that teams at #1 and #2 that have missed have often missed on bigs. Greg Oden, Hasheem Thabeet, Shawn Bradley. Even that stacked 1996 draft had the #2 pick (Marcus Camby) and the #10 pick (Dampier) not make an all-star or all-NBA team when 10 other 1st rounders did.
That actually surprised me a bit and is an example of how this is a very superficial analysis. Camby was a good player . Sure, he wasn't Iverson (#1) or Kobe, Peja or Nash (#13-15) but I'd argue he had a better NBA career than Marbury who made 2 all-star teams and two all-NBA 3rd teams.
So, interesting if not totally clear cut information. Oh, and worth noting. The ONLY year of all 25 that I looked at where not one guy taken 1, 2, 5, or 10 ever made an all-star game or all-NBA team was 1989. And of course, that was the year the Kings had their only #1 pick and drafted Pervis Ellison.