My guess is that the rapidly-expanding vapor and debris cloud produced by the explosion is likely to dislodge and eject more material than would result from a p

My guess is that the rapidly-expanding vapor and debris cloud produced by the explosion is likely to dislodge and eject more material than would result from a passive impactor capable of producing the same deflection. To get the same deflection, you need the same impulse, and in both cases, the impulse is applied as a sudden shock, but if you are using a passive impactor, all the energy is directed in the direction you want the change of the asteroid's momentum to be - so you need less energy overall?