Nice, but goku isn't one to give up sparring someone, even more so a worthy opponent like supes.... Goku doesn't see fight as violence, but a sport. Supes is like rigid righteous fellow, he might entertain goku's challenge or just straight up ignore him...
Was thinking the same, honestly it's more the fault of how the narrator worded challange to the two rather then the two being too altruistic to test each other.
First manga is https://www.mangaupdates.com/series.html?id=156244 I like blasting the song "Don't Stop Me Now" - Queen while reading it. Is fun. Haven't kept up with the chapters in awhile though.