So I was was watching the Sasuke vs Deidara fight and thought about the end of the manga. With elemental advantages fresh in my mind I went to Narutopedia and looked up Indra's arrow and sure enough I was correct in thinking that it was infused with Sasuke's lightning element. It pains me to admit this but if both of Naruto's two attacks had the elemental advantage and still just tied Sasuke's attack, they must have been significantly weaker. Personally I was disappointed coming to this realization but it is what it is.