Please stop playing.
Medical Ninjutsu is the pinnacle of chakra control, there is no fact against this. It requires such precise and minute chakra control that the slightest mistake will unravel it; in fact, an example of this is the very fact that it manipulates the body's cells, which we cannot see.
On top of that, Sakura is a genjutsu-type ninja and genjutsu requires great control as well. Sure, the Rasengan is difficult to use, but it doesn't come close to covering the capability of even the basic healing technique which has so many possible adaptations, WITHOUT added elements. Oh, and she did all of this at the age of 13.
Naruto/Sasuke were granted power from Rikudo without having to train to use it; it was a gift, an innate ability, have you.
They didn't train to master ANYTHING. IN FACT , Naruto only "mastered" Kurama's chakra because he fought him and forced him to fork it over (also making friends with him) not because of chakra control.