what im wondering about is whether they should really make them fight against each other, if we apply concept of "Gu" poison jar, would the surviving natural enemy not be the strongest of them all and in the end they will still be wiped out? unless they somehow become stronger themselves this plans of theirs is gonna send them to their doom. I heard long time ago somewhere, idk whether it was fanfiction or true story, but One had written some story where Boros was main villain and it ended with hero's death in the end which is what caused him to seek out saitama later on, so i wont be surprised if this world somehow ends up destroyed with boros leaving it at the end (Aliens referring to Boros in this case, though it would be big stretch) even if we scratch that, this world is still doomed.