At least Volg managed to become a world champ. Clearly the secret is to becoming champion is to be either the author's pet character (Takamura), or someone he doesn't give a flying fuck about. Anything in between, and you're toast.
I don’t consider Volg as among Ippo’s
closest contemporaries (just an ordinary one) because his circumstances are so different and harsh. He had to leave his country to box and his fights are almost all away from his home country.
On the other hand, the likes of Sendo, Mashiba, and Miyata are more similar to Ippo, they’re all Japanese, doing boxing mostly in their home country, they can spend some time abroad, but ultimately they come home and get a lot of support there, hell, the title fights keep mostly happening in Japan (perhaps for economic reasons).
In some ways they’re quite privileged and to some extent perhaps reflective of the Japanese boxers’ careers that the author has observed (or the ones from his gym).
Outside of all that is as you said, the author’s pet character, Takamura.