I'm not saying this because I am some jackwagon who is jumping off the bandwagon. I was never on the bandwagon. I said it before he was moved to the closer's role and I will say it again—the closer's role vastly under-utilizes Chapman's abilities and he should not be used there.
This isn't 20/20 hind-sight here. Most closers don't face the heart of the order regularly and they more often than not are thrown into "not-so-crucial" situations.
With the type of manager that Dusty Baker is (simple and by the god-forsaken book), Chapman is locked into throwing what is often one worthless inning, starting an inning off to "protect" a two or three-run lead. That's what a closer is to Dusty. Stepping into these situations has caused Chapman to rely on fastball after fastball after fastball.
No matter how good your fastball is, big league hitters will eventually catch up to you.
While pitching in more crucial situations, the "Cuban Missile" was forced to use his arsenal and continued developing his other pitches like that devastating slider.
Chapman needs to be pitching in crucial situations from the sixth inning on, and once he is in, he should be throwing two-plus inning stints.