I think the biggest error in rankings, especially for football, is that they are based on what a 17 year old is today, not what he will be when he is 21-22 years old. Not that there is much you can do about this ranking-wise without a crystal ball, but the result is many late bloomers become the diamonds in the rough and highly ranked busts are often early bloomers. Pro baseball scouts try to account for this when choosing between drafting high school players vs. college players and even older versus younger high school seniors. I’m not sure how much cfb coaches takes this into account, but I suspect the smart and thorough ones are trying to project the eventual strength based on growth rates and genetics.