-He managed to get an old, wrecked Cardassian station's tech to mingle with Federation technology.
-He ironed out the kink's in the troublesome Defiant to the point where Starfleet actually could start making more comfortably.
-Ran an engineering department that not only repaired and maintained a space station and attending starship, but did the same for the dozens of vessels that visited DS9.
-He could do the above in wartime conditions too.
-Engineering wasn't even his original department (used to be security).