none of this is true. He didnt start doing it one handed after befriending kurama, this chapter was the first one handed rasengan, he befriended kurama a year ago. And Naruto never had good chakra control, theyve said that from the beginning, he just has so much chakra it doesnt matter that he cant control it very well. Sakura was actually the one that had great chakra control.
a) In storyline, Naruto befriended Kurama in middle of war, that is, no more than 3 days.
b) Naruto naturally is an adept in chakra control. It was Orochimaru the one who messed up his chakra system with the Seal Jirayia reversed. Proof? Look how Naruto was able to walk over water under Ebisu/Jirayia's teaching, look how Naruto was able to master the Rasengan in few days, look how easy did he handle Kurama's chakra without Kurama's intervention, look how much kage bunshin is he able to create without losing focus, look how Naruto got new variations of Rasengan in his KCM without even training these skills but pure chakra control with Bee as his sensei, and it took just three tries to master the Bijuu-dama (he failed in KCM and he achieved it in BM). If Naruto can't deal good genjutsu moves it's not because lack of chakra control, but because he is too influenced by the Yang chakra of Kurama (and we know already that the Yin part is the one who gives the power of imagination).
c) Indeed, Sakura is the best on the team with Chakra Control.