The Royals no doubt believe that Wade Davis didn't merely succeed in his relief role because he was a relief pitcher. The Royals probably believe Davis actually progressed as a pitcher. Here is a nice compilation of Davis's stuff. There's also a nice ESPN article on Davis and what he learned last year about his mechanics and being able to repeat his delivery. I found the Fangraphs discussion particularly insightful because it dispelled some beliefs I had about Davis's repertoire based on pitchFX data.