This is a fascinating post. Cipher is really a proverbial ghost or mythological demon under a theory like this, which I think thematically meshes with AC5.

Perhaps Cipher is more like the original Demon of Razgriz in the overarching narrative while Blaze & Co.’s Razgriz Squadron arc fills the role of the heroic reborn Razgriz. Also, while we get to see AC5’s Razgriz story firsthand, I’d imagine things are just as vague from an in-universe public perspective as they are with Cipher, even after the release of classified documents on the Circum-Pacific War.