Prove it. I can quite easily prove that not every prospect who gets an Alabama offer becomes a 4-star. Can you prove bias toward the helmet schools?
People want to believe things like this because it explains away the difference between a school like Alabama and a school like Wisconsin. I mean, it couldn't just be that their players (and coaches, for that matter) are a lot better, right? In reality, the average player signed by Alabama is much, much better than the average player signed by Wisconsin. That is why Alabama contends for national titles every year, and Wisconsin doesn't.