When he is healthy he is one of the best relievers in baseball period.
1, it is a huge assumption to think he'll ever be healthy for an extended period of time. In the last 5 years, his highest inning total is 38. And he's coming off a season where he missed the entire campaign. His health is a HUGE question mark.
2, he's not one of the best when healthy, period. He was lights out his rookie year, and to a certain extent, is living off that rep when people talk like you are. After that lights out year, his ERA has been north of 4 twice, and only below 3 once. His whip has been above 1.8 twice, and below 1.2 twice.
Our bullpen is essentially set. Adding a guy coming off an entire season missed, and thinking he can provide something is a stretch. Especially if you really think he's one of the best when healthy. He's always hurt or less than 100% and is very up and down when on the mound. That's not one of the best, by any stretch.