I don't think that Odium had anything to do with the creation of mankind on Roshar. It was stated that "Three of sixteen ruled, but now the Broken One reigns", meaning that there were not two shards on Roshar, as commonly believed, but actually three. Honor is responsible for creating mankind, Cultivation, I believe to be responsible for a few things, the highstorms being one of them. Think about it. The stormwater is better for agriculture, the storms themselves shape the ecology of the world, and the crem is used in many ways. It might be that Cultivation originally began the storms, but like the "Deepness", Odium came and augmented the power of the storms to be terrifyingly dangerous. Honor must also be involved in the storms too, because of the Stormlight and Soulcasting. The ardent's name for the Almighty means He who Transforms, thus tying the storms to Honor. Again, if the storms were purely of Odium, wouldn't the spren be inextricably tied to him, making Syl a pawn? On a side note, Shardlet's post on August 15 states that the two stars that fell were Aona and Skai. I disagree. The two stars might have been the suns of the worlds Sel (Of Elantris), and of Scadrial. This could also explain how Preservation and Ruin's rivalry came to a head; Odium might have visited that world and the influx of power could possibly have unbalanced both forces to the point of breaking.
