I think you are misreading the chart. There is no question from the data that the first 5 draft picks in the first round have an overwhelmingly better chance to have a successful career than (for example) the last five picks in the first round (and beyond).
This article analyzed the 2005-2015 drafts and came up with this career WAR value chart.
View attachment 53599
Yes, teams can find talents like Mayers in the later picks but it is way harder. That's why
this article has the value of picks 1-5 in Rd 1 to be $45.5M, $41.6M, $38.2M, $34.8M, and $31.9M, respectively, while the value of picks 30-35 are $10.1M, $9.8M, $9.5M, $9.3M, and $9.0M, respectively.