Boruto Uzumaki is the main character of the Boruto series, and, just as Naruto had his Sasuke in his story, Boruto has his Kawaki. The two are exceptionally powerful and, more importantly, central to the overarching plot of the Boruto manga. In fact, the very first glimpse that fans see in the story is a fight between Boruto and Kawaki set in the future.
It goes without saying that Boruto and Kawaki are exceptional fighters and, being the main characters, it is expected of them to be incredibly powerful. They have the potential to be the strongest in the entire franchise, however, Naruto and Sasuke, who previously were known to be the strongest in the world, now face a great challenge. With the powers that Boruto and Kawaki have gained, surpassing the legends of the old era might as well be a possibility.
The Peaks Of Naruto And Sasuke
Both Naruto Uzumaki and Sasuke Uchiha are known to have been tremendous Shinobi. In their own stories in Naruto, both of them went on to accomplish great things. Naruto Uzumaki became a perfect Jinchuriki and attained a special bond with Kurama. That was certainly not all. Naruto also went on to receive a portion of every Tailed Beast's chakra. Furthermore, after having the Nine Tails ripped out from his body, Naruto received Six Paths powers from the Sage of Six Paths and all this made him ascend to the next level. At the peak of his abilities, he could use the power of his Tailed Beast as fuel and match up to even the strongest characters, such as Isshiki Otsutsuki.
Meanwhile, Sasuke is known to have been equally as skilled as Naruto. Being a prodigy of the Uchiha clan, Sasuke was blessed with immense talent right from the get-go. With time, he mastered the usage of the Sharingan and then went on to awaken the Mangekyo Sharingan. Following the weakening of his eyesight, Sasuke transplanted his brother's eyes into himself and made his powers eternal. This already made him powerful enough to be considered among the strongest in the world during the Fourth Great Ninja War, however, his growth did not stop there. Sasuke then went on to receive the other half of the powers of the Sage of Six Paths and awakened the Rinnegan in his left eye. In the blank period, Sasuke is known to have trained even further and caught up to Naruto, being a canonical equal of the 7th Hokage in the Boruto era. By the time the story of Boruto and Kawaki begins, both Naruto and Sasuke are known to be the strongest in the world.
The Potential Of Kawaki And Boruto
Boruto Uzumaki, being the son of the 7th Hokage and Hinata, was already predisposed to a strong Otsutsuki chakra. This chakra of his only grew as he grew stronger as well. Boruto is known to have been exceptionally skilled as a Shinobi, even when he was a child. This made him the complete opposite of his father, who was deemed unfit to be a Shinobi at one point. Boruto's powers increased even further with time, however, his true jump to the next level came when he was branded with the Karma Seal of the Otsutsuki Clan. Boruto became the vessel of Momoshiki and, in time, Momoshiki's very own powers were extracted into his body, making him a perfect Otsutsuki.
Similarly, Kawaki had something similar passed down to him by Isshiki, and he became the vessel for the latter, until Naruto Uzumaki finally freed him of that curse. That said, he still bears the powers that were extracted into his body with the Karma seal. In essence, both Boruto and Kawaki hold the power of the Otsutsuki Clan, and, as such, possess enough skill to rival the likes of Naruto and Sasuke. By this time in the story, they have, effectively, surpassed both of them.
How Naruto And Sasuke Got Nerfed
While at their peaks, Naruto and Sasuke would still have been superior to the likes of Boruto and Kawaki, the two have been dealt with in very nefarious ways in the plot of Boruto going forward. Both Naruto and Sasuke have been nerfed several times just to give the next generation a chance to shine and take the stage from them. It can be said that both Naruto and Sasuke have been used as stepping stones on countless occasions in the Boruto series. Boruto and Kawaki have taken the shine from them and, while that is upsetting to some fans, it is somewhat understandable, given that it is their story and not that of Naruto and Sasuke.
In the case of Naruto, he ended up losing the powers of Kurama after his fight against the Isshiki. What's more, it appears that he can also not make use of the Tailed Beasts' Chakra that he had within him for some reason. Naruto has, thus, been severely nerfed and the same goes for Sasuke as well. Sasuke lost his Rinnegan after Momoshiki stabbed it and it appears that he has lost his Six Paths powers as well. Right now, Naruto and Sasuke are far from their peaks and, with Boruto and Kawaki growing continuously stronger, it is no surprise to see them having surpassed these legendary figures of that shinobi world.