As usual, there are studies that show the complete opposite. I have some that I can send you that state that the learning of a particular skill is very specific and that it will not transfer to a different, similar skill endeavour.
Again, Mills understands and believes this too. Remember, all of Mills' trash talk about throwing being the best to prepare the body to pitch is AFTER a level of overall fitness is reached, including balanced strength about a joint.
His views have been like they are now for quite a while. I don't recall him saying that strength and weightlifting are "bad", only that a focus on arm strength is futile. He is OK with weightlifting in the context of the overall body fitness he espouses. It's being "arm specific" that he doesn't like.
He would argue with you that he is just the opposite of "opinion", that he is the only one out there NOT just giving opinions. That really is his marketing pitch.
His latest thing is to say that his approach is now totally based on the valid scientific studies that exist out there. The book he wrote with Rushall is based on their review (which is where they can be wrong) of the studies out there, Rushall's evaluation of their validity re: scientific method, dismissing the ones that don't stack up, keeping the ones that do and then basing everything they do on those. Now, the potential fallacy in all of this is that the evaluation phase of that approach is completely by Rushall. He hasn't gotten independent verification of his evaluations. Rushall, as far as I can tell, is fairly credible and before dismissing his evaluations, someone needs to read them. Too many people are dismissing them solely because they don't like Mills. Read them and then evaluate the evaluations.
Having said that, are you saying that everything said on this, or other, sites is NOT "opinion"? I'd say it's ALL opinion. Where's the evidence or backup for anything said on this site?