The top 15 routinely has the highest hit rate. They are lottery tickets where some have more likelyhood of yielding a prize than others.
2000 draft: 10 Pro Bowlers in the top 15, the only HOF'er in the draft class. Tom Brady will end up being another HOF outside the top 15. Outside the top 15 there were 18 Pro Bowlers. So you have a 66% hit rate in the first 15 picks and a 7% hit rate outside of it.
2001 draft: 9 Pro Bowlers in the top 15. Including 2 HOF'ers. 25 outside of it. Again huge disparity.
2002 draft. This was a weak one for the top 15. 6 Pro Bowlers. Outside of it, 13. So in the top 15 you had a 40% hit rate. Outside of it you had a 5%.
2004 draft. This was an all time famous draft. 10 Pro Bowlers in the top 15. So again 66% hit rate. At least 2 HOF'ers. 21 outside of it. So an 8% hit rate.
2005 again had 10 in the top 15.
2007 had 8 in the top 15 including three HOF'ers.
2011 had 11 so you are talking a 73% hit rate there.
2013 was an outlier draft. That's one where only 4 guys in the top 15 became pro bowlers.
2014 had 11 again.
As far as the number 1 pick, since 2000, only 4 number 1 overalls didn't become Pro Bowlers. Courtney Brown, David Carr, Jamarcus Russell, Sam Bradford, and Baker Mayfield. Mayfield was the only non probowler #1 overall since 2011.
It's just ridiculous to say those aren't high commodity picks. At any given time, almost 2/3rds of the leagues QB's are generally top 15 picks.