The thing is, it doesn't matter if it's 2 Rasenshuriken or 1000. Naruto poured all of his remaining chakra into those two Rasenshuriken. Meaning the power was divided by 2. If he made a thousand of them, it's still the same collective power, just divided by a thousand. This is evident by the fact that Naruto felt rejuvenated by Kurama, and then was out of charka again after the clash. Naruto's killing intent that moment is pretty clear by the fact that he poured all of his chakra into that attack.