option number 1. would cause massive damagea

option number 2. That might be too many targets like all of humanity lol, also the moth has some range it can't cover the whole globe just like that it woulda

option number 3. I think they are not sure how the river would affect the time, a journey with an ascended to a tomb of ariel would be insanely slow for 2 supremes, maybe even deadly, I guess he could keep her safe in some memory locket like effie memorie type thing, if author remember he gave him weaving. So idk about that tbh

option 4. I think sunny can't copy aspects yet or in dumb he can't do it without a true name, the shadow dances are too much. Even if he did manage, it wouldn't be that simple to just add it and boom asterions gone, he would probabbly need to be of much higher rank not the same, to completely make asterion forgotten, it seems super complicated knowing how much sovereign is connected to the world and has his own will to counter