It's the same with KenPom in basketball or recruiting rankings. If someone takes the system and applies it as the bible, they'll be wrong. In both cases, the creators will admit that there are some factors that we just cannot judge and there is also just variance in real life, of course. That said, all of this stuff is "as good as we can get." Those are excellent systems to approximate with. I just laugh when I hear someone say, "recruiting rankings just don't matter! Look at all of those 2-star guys in the 1st round of the draft!" Well, yeah, they still are correct given that there is a much higher of 4 and 5 star guys. Rivals or 247 will admit to you that it's impossible to be much more exact than they currently are with 16 and 17 year-old kids...but it's pretty darn good overall. I'd rather have it than not have it.