This will be moved, if not outright deleted as trolling(just my opinion, but it has the feel and is a 'drive-by' post) but you fail to realize what the all hero mythology is, or the fact the DF is by and large based around the idea all stories are simply different renditions of each other. But consider instead only the fact that both are writers and both went to college for it(I confess, I'm only assuming Martin's schooling). I'd say it's likely, especially when dealing with mythological make up, they actually drew inspiration from having read the same great stories.
Draws my mind to one vid about magical systems where one of the authors makes a point to ask about a handful of writers and if anyone in the audience has ever even heard of them, to a general reply of no. Then asking if his fellow authors have read them to a resounding yes. An that's the difference between reader and writer that Butcher and Martin share and you may lack, despite reading a bit on Tam Lin wiki