the Main Character is *per defenition* important to the story. Even if that character would not exist if not chosen as a Main Character.
This does not make any sense. How can a character that may not even exist in the story be important to the story? If a story can be told without a particular character's existence, then that character is not important, by definition.
This is why 'Tav' is NOT at all the same as 'Charname' because although Charname also could be defined by the player in whetever way they wanted, Charname as a person always exists in every playthrough. But Tav may or may not exist in the game world. That makes Tav expendable and superfluous to the game's story.