In addition to the analytical faults, the notion of "pulling their weight" has all sorts of moral imperative baggage which is more typically used in the context

In addition to the analytical faults, the notion of "pulling their weight" has all sorts of moral imperative baggage which is more typically used in the context of the free-rider problem from game-theory. At the very least you'd have to make a strong argument that any nation has an obligation (which is what "pulling their weight" refers to) to help.