I don't know how Moses wrote his "song", but I hope the tune was catchy because the lyrics are not easy for me to remember. I do find Moses' final blessing for the tribes unusual. There are only 9 sections of the blessing for the 12 tribes plus he kind of gives Reuben a blessing ("Let Reuben live"). Reuben was first born and is mentioned first but had lost rights of the first born after sleeping with Jacob's concubine (Gen 35:22). In many circumstances Reuben is replaced in the 12 tribes because Joseph gets a double portion through his sons Manasseh and Ephraim. Reuben does get an inheritance (chunk of the promised land).
Anyway, the order of the blessing is usually important and the first real blessing is to Judah, the fourth born. Levi (3rd born) is next followed by Benjamin, the youngest. Joseph then gets the 4th blessing, which is strong enough to a blessing of the firstborn, but both Ephraim and Manasseh are grouped together. Zebulun (#10) and Issachar(#9), Leah's youngest son's, are also grouped together. Asher (#8) is called "the most blessed of sons" but gets the last of the blessings. Simeon who is second born and should be the heir apparent isn't even mentioned.
I just found the blessing unusual.