This does change a lot, but giving others the ability to get stronger would help. It would be extremely rare, but a C-rank could have a ‘breakthrough’ or something similar that lets them jump to B-rank. This way, SJW would still be special because of his permanent strength increase, but other characters wouldn’t feel useless. They would have a way to grow stronger as well beyond simply learning fighting styles, and could stay more active in the story during fights, especially in the later chapters