You're making what may be an incorrect assumption about Dylan Cozens. It's not clear that Cozens is, or ever was, a "primo prospect." Cozens has great power - but his difficulties with the strike zone? That's not "regression" in 2017; that's been there all along. I think most of us recognized that AAA was going to be a real test for Cozens, because even in his "great" year in AA, his strikeout rate was conspicuously high. Cozens had to contend with AAA pitching this summer - and AAA pitchers (especially the older, AAAA-types who don't rely on fastballs to blow people away) tend to take the measure of free-swinging guess hitters.
I don't see that you can fault Wathan for not somehow gifting Cozens with strike-zone judgment, and the ability to recognize, and lay off, pitches he cannot drive. While we've certainly hoped that Cozens would develop some such judgment, he's never had it - and we can't assume that "better coaching" can change that. Some players simply cannot identify and lay off such pitches; they depend on guessing correctly, and hitting mistakes. The difference in 2017 is that Cozens ran into pitchers who have the capacity to throw stuff he cannot drive, but will still swing at.
