You made a couple of good points if superman uses his speed he can beat anybody, but usually as we see superman he doesn't use his speed or use his powers to the fullest. Other than the DBZ epecially goku who uses their power to the fullest. Superman beating goku is like saying superman can beat batman. Batman can beat superman because uses his brain and that is his advantage. Superman doesn't use all of his powers. Like I said other than goku who some people think he's an idiot, but is very smart in how to use his powers. Your comparing a hero who came from krypton who doesn't use his speed, can move a planet, survived a super nova. To a guy who was powerful before he was born, can destroy a planet which is much more powerful than a super nova, actually he can actually destroy a universe.
So you go from saying that Goku is stronger/faster/better, to saying "OMG GOKU WINS CUZ SUPES DOESN'T USE ALL OF HIS POWERS!" Yeah, fumble for more excuses to save Goku.