Cahill has not been good for the majority of his career. He's not as bad as his ERA but he walks WAY too many batters for how few Ks he has. Guys who walk 3.5 batters per 9 cannot K 6.17. His only redeeming quality is as a groundball pitcher sometimes those walks get negated, the downside is as a ground ball pitcher you let more hits fall so those walks can be amplified (like we're seeing this year)
Sure, highly unlikely he is a really good starting pitcher but I think a mid rotation innings eater is still possible.