The other thing you need is patience, Kluber is a perfect example, at age 24 he was having a solid season in AA when he got traded to the Indians, basically a second tier prospect with limited upside. At 25, a so-so season in AAA ball (4.53 FIP), pitched better in AAA ball the next season and got promoted into the Indian rotation and became one of their starters in 2013 at age 27.
His FB/sinker has always been pounded, when he came up his slider was his only plus pitch, a solid curve which he rarely threw, and a changeup that was a work in progress. The last fews years the sinker improved slightly, but what really made the difference for him was the curve, which went from an afterthought to an out pitch along with his slider.
Point is you stockpile young pitchers and provide them with excellent coaching, because mastering two secondary pitches along with locating a decent FB is all you need to be dominant, curve, slider, changeup or even a split finger. Master one and you can be a dominant RP, master two a top of the rotation starter. We saw this with Cliff Lee.