Ah...quick comparison from Corbin 2017, 2019, 2021: hitters have always hit his fastball, but hitting it better this year. Bouncing around .280 and now well over .300. They also have always hit hit sinker. Cannot hit the slider, which they hit at about .155 in 2019, but they are up around .225 or so.
Looks like batters have always hit his sinker and fastball. If he can't get hitters out with the sinker and fastball, and if even his slider is a little more hittable, he is cooked.