Board Thread:Naruto Discussions/@comment-44437908-20200507051002/@comment-30323490-20200519185748

Every main character from the Naruto series got powerups from external factors: Naruto obviously had Kurama from the beginning and eventually received chakra from all bijuu as well as SPSM from Hagormo. He still however has his own trained powers: rasengan, multi shadow clone, rasenshurkien SM which would put him to Kage level (even High Kage level by adulthood).

Sasuke got a bunch of external power-ups : The curse mark from Orochimaru, then he even absorbed Orochimaru for a while, then he took Itachi's eyes to unlock EMS, then he received rinnegan from Hagoromo and even in the final battle he got power-ups from all bijuu. He would still have 3 tomoe sharingan and MS (assuming uses it moderately and doesn't go blind) which also puts him Kage level-ish.

Boruto obviously has his Karma stuff going on and probably had the jougan given to him as well somehow.

So it's a recursive occurrence to get external power ups....