Fact, now I aint a Sasuke fan boy or a Naruto fan. But Enton while enhanced by the Rasenshuriken did not have anything meaningful added to it by naruto's help. The amaterasu flames basic nature is what makes them dangerous. They continue to burn for 7 days nights and they spread.....
IE while the Rasenshuriken initially increased the hitting power and spread of the combined jutsu it did not contribute to the lasting properties of the jutsu where the meat of the attack is which were all in Sasuke's ball park.
IE if Sasuke had attacked on his own, while the amaterasu arrow would have struck with minimal damage and spread, the flames however would spread to encompass the enhanced combo's initial attack spread and beyond it. So Sasuke did kinda solo the juubi.
