FWIW, I remember PECOTA being very very low on Maton heading into last year's season.
Edit: I just looked it up. He actually exceeded his PECOTA last year. I stopped buying their annual, but their website archives their player comments. Last year's on Maton was spot on:
"When Maton hits the ball, he can really hit the ball—he sees four-seamers expertly and crushes them with abandon. The problem, unfortunately, is what happens the rest of the time. He chases breaking balls and off-speed pitches on both sides of the plate, and he strikes out a ton. Thus, he's a much better hitter when he gets ahead in the count, but he tends to fall behind far more often. His defensive versatility is an asset, but he isn't elite at any position. Maton provides flexibility off the bench, but his shortcomings on both sides of the ball prevent him from offering a whole lot more than that."