Fact Sakura has always better use of Her chakra but next to the large reserves of Chakra that Naruto and Sasuke carry naturally inside them She is a water pistol. Sakura may be able to use let say 90% to 99% of Her chakra with little or no wasted but She is like Kakashi both are curse with having a small gas tank compare to the gas tank Naruto and Sasuke have, they can afford to use up chakra and still have plenty left to finish the job. Because of this Sakura will hit a wall in development as Kakashi has, they both have to make sure they don't run out of chakra and life force against the big guys and gals out their.