I admit I haven't read the Challengers' Archives, but if you say that they battle intergalactic threats to the whole world, I'll take your word for it. But then, I actually think that makes this story even more senseless.
To my understanding, this story is stating that the superhuman makes the human obsolete.
If the humans in question have proven able to take on, and actually defeat, intergalactic threats to the whole world, how on earth does the introduction of superheroes make them obsolete? Why couldn't the guy in the story fight alongside the superheroes, instead of retiring from his life of adventures and going on to live a quiet, bitter and resentful existence?
It seems to me like this story wants to have its cake and eat it too. "Superheroes make human heroes obsolete because humans can't compete with them! Even though human heroes can totally perform the same deeds as superheroes do!"
Batman (even before he became the Batgod, when he really was just an extremely skilled and intelligent human) never stopped fighting just because his world already has Superman, Wonder Woman, Green Lantern and many other god-powered heroes; instead, he makes allies with them and they fight all together against evil. If he can do that, so could these Challengers guys fight alongside their superheroes. If they chose not to, that's not the superheroes' fault.