Of course Kimbrel is special. But he's a closer. Look at Lidge, Gagne, etc. many guys have been dominant and then fallen off the face of the earth. Many guys like Papelbon started dominant then faded as time went on. For every comp to Rivera or Wagner, you can comp Kimbrel to a lesser closer.
Also you have to remember Billy Wagner was traded, yes he was older but there is positive value to that in that he had proven health and long term dominance, no falling off. Astros got for him Brandon Duckworth, Ezequiel Astacio, and Taylor Buchholz. the peak ranking of those guys are Astacio at 80, Buchholz at 50, and Duckworth didn't rank at all. So to compare those to prospects from last year, would be like the Yankees offering Gary Sanchez and Tyler Austin with a nobody. DOesn't get me out of bed.