To get down to the nuts and bolts of it, I don't wanna say he's a product of his home park/weak division but I think it plays a decent role. I wouldn't say he's as bad as some pitchers we've seen in the past but I think something is there. All of his underlying numbers pretty much suggest a pitcher who should be equivalent to say Blue Jays Burnett in his last year there. Still good. But he's one of the only pitchers that regularly outperform his peripherals (which is why I call him an anomaly of sorts). His career ERA is like a full run below his XFIP and he always gets somewhere around 12-15% infield fly balls when the rest of the league averages under 9%. The park suppresses his HR/FB rate so much it's absurd, think it was like .37% last season (same with his BABIP). I shouldn't specifically "call out" Cain but there's a long list - Lince, Lowry, Schmidt, Ortiz, Tomko, etc. Plus, IDK if he maintains the spike in GB% that he had last year. I think once those abilities are gone, he may be a sunk cost.
I thought resigning him was a mistake because with their park and pitching coach, they've had a lot of success getting cheaper pitchers and turning them into usable parts. They don't have to pay market value for a stud SP, they should have thrown that $22 million at a stud hitter.
I don't wanna sound like I don't like him because I know he's better than all those listed pitchers. He has an great K% that's always consistent and the fact that he does outperform those peripherals speaks volumes. IMO just not worth $22 million to them.