I'm not a football professional, so I can't speak to the scouting side of things, but I can speak about statistics with authority. What Bales is saying is misleading. First of all, it can't be proven that individual drafters return to the mean with the quality of their picks, it can only be shown that there is not sufficient evidence that they pick better than chance. Those are two very different things. Even if this could be proven, the picks you make one year are not independent of the picks you make a second year, and so any causal explanation is questionable. It may be harder to pick successfully in the draft if you have been successful in the past for some reason - that is an alternative explanation for returning to the mean.
Secondly, the kinds of statistical analyses that can be done in football are limited by the small sample size of much of the analysis. Statistical findings may be non-significant due to something actual not being significant, or they may be non-significant due to a lack of statistical power. Statistics are generally used in football in situations where there is a large enough sample size - so you might group football players historically according to position and examine objective measures that predict success at that position. You can't use statistics to analyze more specific situations - how well a drafted player will do as a 1 technique under Marinelli - because the sample size will be too small. Also, there are a lot of subjective and arbitrary decisions that need to be made in a statistical analysis - like defining the success of a particular player, or deciding how far back to analyze players.
Bales seems to say that using predictive stats is better than scouting for the draft, but there is absolutely no evidence for this. He can say that his predictive stats better predict player success according to some measure of success historically, but that is a lot different than having to go pick the players yourself. A lot of the specific factors that get averaged out in a large analysis come in to play when you are the GM of a specific team. Or to put in simple terms - the best player for the average NFL team may not be the best player for the Dallas Cowboys. It probably wouldn't even be possible to really test Bale's hypothesis, because if a lot of teams starting picking in a Bales approved way, it would change the nature of the draft and the historical data wouldn't be predictive anymore, and if only a few teams did this, then it would take too long too build up statistical power to test his hypothesis and the game would have changed by then anyhow.