I believe the statistics would show that there is a strong correlation between recruiting class rankings and success, however there is also grade inflation when recruits go to helmet schools in some circumstances.
However, I think the points Coach Kill makes are the same that apply to ACT and SAT scores which are a lot more fact based than football recruit rankings are. Higher college admission scores generally predict success in school, but there are a lot of exceptions. They are less effective in predicting professional success, even though there is some correlation, because they do not evaluate social intelligence and motivation.
Given that recruit rankings are more subjective than college entrance exams, and that the recruits success is greatly influenced by their fit in the system used at the school, there are a lot of reasons why a kid going to a specific school may do considerable better or worse than their ranking would predict. When you look at a school like us that has had a different "system" every year there is no system designable by man that could effectively predict success in our program the last four years.
I think kids being recruited to the wrong system could explain a lot about why kids are misevaluated, plus some kids have a lot more potential for physcial development after high school, and others are pretty mature physically. I am always amazed at how old some of these kids look in high school. Jenkins looked like he was 28.