But his slider used to be his best pitch. Granted, his command of it was spotty at times, but the movement profile was elite.
The change-up has followed suit with reduced effectiveness (batters hitting .306 off it this year). My assumption is that the change-up played really well off his slider as his other off speed pitch. Now that he has abandoned the slider, the change is all he has left for an off-speed offering. Add to that, his FB has lost velocity. Although it's effectiveness has actually increased, but again I go back to the HR rate being abnormally low.
Basically, he is a FB/Sinker pitcher at this point, and he throws a decent change to keep batters from sitting on those 2 pitches. That isn't going to get it done as an elite closer. He can still be effective, but he's nowhere near an elite RP anymore. Maybe if he recaptures the slider, but at age 35 that seems unlikely.