To me the main reason why we're keeping all these Hellenistic factions is to not throw away the work that's already been done. I personally would probably have preferred to have fewer Hellenistic factions, and perhaps add one or two others, but it's not really the matter what I or anyone else think personally. What matters is what makes sense for the game, and from a development point of view. To me it's hard to argue for adding more factions as it's a lot of work even maintaining the ones we have and make sure they are as interesting to play as they can, and will be as balanced as they can be. I still don't think it's a good way to go to remove factions we already have though. Both because that would mean that the work put into them would have been wasted, and because we have said that the game will include these civilizations. Sure sometimes you have to change things, and remove things, even though you have said they will be included, but to remove something just to add something else instead doesn't seem like a good way to go.
While I sometimes do use the word civilizations as well I prefer factions as the word civilization has some problematic connotations, i.e. is a group of people more or less civilized, or for that matter how do you define exactly what group of people is a civilization. A faction is simply a group that's been set apart as a unified group for this game, so it doesn't carry the same problems.