Me_Writer
I am not sure if anyone has mentioned it but to cross the power bridge between him and s class with his lack of magic why not try for the realm of the great swordsmen as its called by fans from one piece (using a mysterious energy not magic closer to sword intent) he has the basics of it capable of creating air slashes without magic, he just needs to continue to deepen his understanding of the swords and he will not only have the power to slice mountains and split seas but he will be the hero of swordsman everywhere putting the power of the sword truly on par with the strongest magic. Also for his magic strength of 100 seal from naruto, some time of magic storage seal drawn on his body maybe using the blood of powerful demon beast as a medium .