There are a million reasons why macalister is not red john.
My biggest red flag was his fear of dying.
I know that even crazy people crumble in the face of death not red john.

William blake was gnostic. If i could explain gnosticism at its core in one sentence it would be that man is god. And that there isnt a man with a beard in the sky that judges people.
Red john does not believe he wi be judged or go to hell.
Macalister was a pawn.