I like the theory but go a little deeper than that look at your planets which might have a population unknown to earth and the leaders of those planets could meet and just like the country's of earth may not completely get along; hence the split between light and dark! But they might also be dying off as part of the raids to come! Look at oryx for example in the opening cutscene the queen knew the danger of oryx! Maybe she knew he was on a hell bent path of destruction and as a follower of the light in the nine she was tasked to defeat him! Why else would she unleash that weapon that she did, based on the danger faced during previous parts of the game she could have single handed my destroyed everything she wanted with out any trouble in doing so! So maybe oryx was part of the nine and since you the guardian has killed him now there are only 8