What I am wondering about is why the fused ever agreed to be invested by Odium in the first place. If I followed the timeline correctly ancient Dawnsinger welcomed Human, at this point they are not of Honor/Tanavast but of Odium and come from a world they ravaged by using their power. I am not clear if it by surgebinding or voidbinding, but I am rather convince it is voidbinding since surgebinding is from Honor and since ,even without the Herald warning, surgebinding appear to be a investiture system who regulate itself in opposition to voidbinding. No hard proof there.
So they welcome the son of Odium being urged to do so by their gods, is it Honor and Cultivation or just the spreen? If so is it the spren of Odium or the Spren of Culti and Honor?
Humanity is confined to present day Shinovar, and at some point (speculation from me) split into two group those who do not leave Shinovar and are bound by the original "pact" the Shin and the other human who spread to Roshar. Then conflict erupt between Dawnsinger and those human, I highly suspect Odium and his unmade to be the driving force of this conflict.
Loads of question here, are human voidbinding at the beginning of the conflict ? what power do the Dawnsinger have at their disposal to pose such a threat to human that Tanavast decide to side with them through the heralds. Since the Radiant and surgebinding appear much later after a few desolation.
Regardless Odium end up investing Danwsinger making them Fused , but why would those accept? Odium is foreign to them , most likely the cause of the conflict, apart from this form of "Immortality" I don't really see why the would side with him.
Edit :
Nevermind it appear that the Human of Roshar were not from the 3 shard, that Odium came to Roshar after the human settled their, that human were interested in Odium more than the Dawnsinger , which might have been why a conflict arose.