Except Naruto couldn't have used 9 Bijuu Dama Rasen Shuriken. He used the Nature Energy Kurama gathered for him to buff his Avatar and create 1 Giant FRS and 1 Bijuu Dama Rasen Shuriken. 3 Avatar hands were needed for each, thus he can only make 2. 6/3=2. Not to mention it created a far larger explosion than the 6 Bijuu Dama Rasen Shuriken he used, meaning the quality of this attack>>>>Quality of the rest of his attacks.
Punch his arm off? He cut it off with a chakra arm, and by the time Naruto had access to Sasuke's body, their avatars had been destroyed and they had reverted to base due to chakra loss and heavy damage. Base Naruto can't do that, and that explains why he didn't use Sage Mode, not enough chakra to enter it.