> a man that claimed to be God is either a liar, a lunatic, or God; to say such a man is a great teacher but not God stretches the limit of rationality.

I don't really get this. Someone who thinks they are God and isn't (the "lunatic" part) can still have important insights and a knack for showing them to others. Someone who knows they are not God but claims to be (the "liar" part) can be using their lies to spread valuable insights more broadly. I would definitely prefer to learn from someone unencumbered by either issue, but they don't seem fundamentally incompatible with being a "great teacher".