Although this port is good in that nothing sounds off or out of place, it's bad in that the only two things that have been done in the MML from what I can see and hear is the optimization, and instrument selection. There's a plethora of extra commands and effects in AMKs readme that could be experimented with this port to prevent it from sounding too basic, such as echo, vibrato, panning, and custom ADSR. Those are just examples of commands that can be used that I'm naming. You don't have to use all of them, but the one I'd highly suggest you look into is custom ADSR.
That's pretty much the only reason why it's getting rejected. I'd also watch the optimization as single note loops that repeat less than 5 times [[d4]]4 is more bytes than when it isn't looped: d4d4d4d4
Now I noticed in your submission notes that it's supposed to be a SNES recreation of a NES song, but what you may not know is that an official SNES version of this song exists. I'll link it here. I figured I'd mention it in case you end up wanting your port to to resemble the SNES version of this song.