Originally, Naruto was only able to apply Nature Transformation to his Rasengan by using two Kage Bunshin to split it amongst three separate steps in its formation, because he thought of it as looking in two directions at the same time. A TON of chakra had to be kneaded and split amongst himself and the two Kage Bunshin to accomplish this, which is why Kakashi said this was a method that would be impossible for him, or Minato.
When he started making Rasenshuriken without Kage Bunshin once he gained Kyūbi Chakra Mode, he was using two additional chakra arms in place of the Kage Bunshin. When he gained Bijū Mode, he didn't even need the additional chamra arms—though it could be possible that Kurama's cooperation, or use of natural energy could have played a part... THEN he was shown making Rasenshuriken single handedly without any Bijü chakra, or Senjutsu in the movie, and everybody's just confused. NOW Boruto is just being made out to be this lil' super prodigy, and has so little difficulty applying Nature Transformation to his Rasengan, that he does it subconsciously. And then everybody just gives up trying to reason how this supposedly impossibly difficult process of kneading chakra is being simplified.
... ANYWAYS, episode 65 was pretty great.
