I prefer to think that Aeron thinks of himself as the true leader of the evil gods, but that Ceridwen is manipulating him just like Agares and everyone else. She probably also has Mammon convince that he is in charge, but he like Ceridwen prefers to rule from behind the scenes.
Agares however is not completely worthless. He may serve mostly as inspiration, but I think that he may provide a certain spark of genius rather similar to his antithesis (Amathaon) that gets most the evil plots started. His focus is on corrupting rather than destroying, so rather than fight he tries to make peaceful contact with good angels. He has proven remarkably good and convincing them to abandon Good, as shown by the size of the armies and the fact that he did not create anyone in them. I do however still tend to think that the sphere of Despair continues to pull him ever deeper, so he is becoming more and more withdrawn from the world.
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I think there may be some merit in Xienwolf's idea that the ritual Trenton Majosi used to try to save his people may be what doomed them. It (and The Draw, which may be the same thing) bears a resemblance to one of the Spells of Winter that Tebryn Arbandi was casting in Kael's D&D campaign. (The campaign is far from cannon, but is the source for many of the ideas that eventually made it into the mod.) The specific ritual I'm thinking of involved killing an entire race of people and consuming their souls for power. Tebryn's allies Auric Ulvin and Tuoni had very different ideas of how this power should be used. Tuoni was having Tebryn use the ritual to kill everyone in the whole world, so that he could capture their souls within the Opalus Mortis (the Gem of Death, one of the Gems of the Creation that long after being stolen from the True Heaven by Agares was stolen from Agares by the mortal Three Brothers) and use the power to create a new world of the dead and make himself the new God of Death. Auric wanted the ritual to stop after it was fully powered but before it could be completed, so that the energy it had collected could instead be used to power his ascension to becoming the new God of Ice. The human players were forced to choose between helping one of these two evil men become a god and conquer the world. They considered Auric the lesser of two evils, and so the precept of Ice gained a new avatar. Xienwolf's idea is that Trenton stopped casting the ritual not so much because he realized the horrors of the new godswar it would cause, but because he at the last minute figured out how it worked. By then it was too late to completely shut it down, so even though their god did not enter Creation the price of the souls of his people still had to be payed. When the Illians discovered the ritual, they found that it had already been almost fully powered and that they could finish it to summon Mulcarn with only a few souls, probably less than they thought they would lose if they let the mad followers of the recently fallen Bhall continue to rage against them. (They may have not realized that the ritual required the death of the victims' souls rather than just the body, so they considered it a small price to pay to kill a few of their friends to save their whole nation.)