Weak conclusion? Are you saying that a non-Catholic can not only be the visible head of the Catholic Church, but also teach heresy to the universal Church?
No. I’m saying that Popes are not infallible in everything they say. Francis is quite fallible in some of his teaching. Where do you get ‘A pope cannot teach heresy”?
I agree they shouldn’t, but I’m unaware if any auto=excommunid=cation when they do. Might even not be a bad idea.