Here is a summary of my argument: if partisan groups like oligarchs and democrats successfully achieve some degree of justice, it must be the case that they exhibit some degree of that virtue as it is analyzed in Nicomachean Ethics Book V (=Eudemian Ethics Book IV). Justice there is divided into two types: justice as lawfulness (which I will often refer to as “justice in the broad sense”), and justice as the equal (or, alternatively, “justice in the narrow sense”). The former type of justice is complete virtue with respect to others; it is the virtue that allows individuals to exercise any of the virtues in a manner that promotes the well-being of fellow citizens. If partisans have some degree of justice in this broad sense, it must be that they promote the welfare of other citizens to some degree. Yet I will show (in section V) that Aristotle does not think that partisan justice is capable of securing happiness for anyone, and thus fails to be just to some degree.
Skultety, Steven, "Is 'Part of Justice' Just At All? Reconsidering Aristotle's Politics III.9" (2006). The Society for Ancient Greek Philosophy Newsletter. 383.