I think he does have more upside. The foundation is so strong - a lefty who can sit 95+ and get by throwing fastballs like 60% of the time. The guy literally only needs one more wrinkle in his repertoire to start limiting home runs. Just something, anything, to get the hitters off his fastball just a bit. Doesn't even have to be a changeup. And he has so much experience, he has used curveballs, changeups, and sinkers more often at various points in his career, so it's not like he is starting from scratch on anything; he knows what works and what doesn't, for him. Just go back to the lab in the offseason and find one more wrinkle.