But if a state has sufficient personnel to handle an emergency (say a tornado strike on a town), they have too much personnel the rest of the time. Whereas, with a governmental entity, they can go from emergency to emergency, keeping wasted resources to a minimum.

The governmental agency can also shift resources from one state to another without having to wait for the resolution of aid politics between the individual states (not to mention the states the aid would be transported through).

Of course, there are significant inefficiencies that exist in those entities in reality, but what would realistically prevent those same inefficiencies from existing in a state-run system as well?