I really like the skirmish rules and was wondering if the three expansions that have different houses can be used as a standalone army against another major house or another expansion, or is it just a supplement to add different units to a major house. For example could the lords of river be used to in a skirmish against the Lannisters and could it also be used against the Tribes of the vale?

I have read somewhere that you would need two sets of an expansion to have enough troops to use it as a stand-alone army.