Well in his defense, Naruto had difficulty with his chakra control (sakura was a genius at that, and sasuke had the sharingan) and lost control of his consciousness when he'd exert himself too much, allowing kurama's chakra to seep out.
The fact that he was actually able to teach him new variants if the rasengan and better chakra control are success stories in and of themselves.
The fact that he was actually able to teach him new variants if the rasengan and better chakra control are success stories in and of themselves.