I think everyone is an alter. I don't understand how there can be a "main". I know I am not "the person" that was born. None of us identify as that. Every single one of us can only do the part of life that we do.
What is the definition of a "main"? The one who is out the most? That would be me, but I never experienced being in the childhood home as "myself" so how could I possibly be the main? I have only been out the most for a few years at best, and others in here would probably argue with that statement anyway.
I just don't know how any one of an "us" could consider themselves to be the main. That isn't how my system seems to work anyway.