I think you need to look around the fact that Epiros was bested by the romans. Epiros would have become a much bigger player in the mediterrainian had Pyrros not had to face the romans outside Tarentum. If Epiros had had the freedom to concentrate their forces elsewhere who knows how powerful they could have been? Whereas in contrast the Illyrians were a tribal pirate nation...maybe with some potential, but unlikely to ever become a world power. All in all i think epiros is included and not Illyria just because its about what they could have been, not what they were. Games are about changing history's path