They aren't the same song because of the tempo. As one comment on YouTube there said, the two songs have very similar, if not the same, structures: "the notes change up at the same points in both songs, even though the actual melodies are different". This is what the video is trying to explain. Regarding the variety, it's true that all the music heard 'til now has celebratory vibes to it. No menacing sounding pieces like Scrap Brain Zone, or calm paced songs like Lava Reef Act 2 (the closest thing to 'calm' we have is Stardust Speedway Act 1). But it's also true we haven't heard the whole OST yet, not even half of it, I think. EDIT: Holy shit, that Jumping Flash song is pretty fucking uncanny, at least the beginning!