"The first two things that pop into my head are: Why the heck has the AL since 1975 been consistently among the highest rookie percentages in major league history (and yet it has a very low failure rate most of the time and hence rates as a typically "major" league throughout that whole period)? "

His conclusion does not seem to match the data he presented as the NL has a higher rookie percentage than the AL and a higher failure rate since 1975.

I meant " ......and a lower (not higher) failure rate since 1975."

Fascinating. Thanks for the link.