It can be summed up like this.
>MCs based on how involved they are in the story
MyGO
>Anon
>Soyo

Ave Mujica
>Sakiko
>Mutsumi/Mortis

>Plot-related MCs, aka "true MCs" (passive MCs mostly, but high importance)
MyGO
>Tomori (MyGO's identity)

Ave Mujica
>Sakiko (very high importance in both MyGO and Mujica's plot)
>Uika (Mujica's identity)*

*Uika wrote the lyrics, and the unmasking theme of Ave Mujica parallels her story. In a way, she’s no different from Tomori in terms of relevance within their groups. And also, S3.