Indeed. I think that this will mostly be a problem depending on how the game handles the Hellenistic kingdoms. If the various Diodochi can mobilize their full potential and use non-Greeks on the same basis as Greeks for their support and armies then, yes, we will probably look at invincible Hellenistic kings. If it can be managed somehow that the Diodochi only get full benefit from the Greek population and less benefit from non-Greeks, at least until certain reforms and stuff has been passed, then they may be more managable.