Yeah, it'd be better if they just gave a reason for the earthlings to have progressed that much, therein explaining from a power perspective them being chosen instead of the kids. Still dumb though as the earthlings and fucking Roshi reaching that level of power is laughable. I think they don't even know what the feats they showcase the earthlings achieving mean, though... if asked, the directors would likely say they are still way behind Namek Freeza.