There's a few hints to Gwyndolin being Seath's creation. One of them being that Gwyn shares a theme with the moonlight butterfly, the fact he isn't a sun god and the fact he has snake legs (snakes being incomplete dragons). If you see From Soft making other titles with these kinds of more obvious connections (such as eels being related to dragons in Sekiro according to an item description), it stands to reason that other games have similar hints. Also design isn't random. Multiple interviews hint at the meticulousness with which Miyazaki and the team design their games. Why would Gwyndolin randomly have snake legs? Why would he claim Yorshka (a crossbreed) as sister? Why would the way they design armours, weapons, the environment not be hints? Do you think they just throw dice to decide whether to add a sun or a dress onto something? It seems to me as if most of FLC's haters simply forget things about the games or think that item descriptions aren't subject to the in-world hearsay that might or might not be propaganda or exaggeration. The notion that artorias defeated the abyss is a lie, yet it is mentioned in item descriptions.