I’m not convinced.
I supplied a link to a book by another sedevacantist (Kelley), which questions the mental state of Thuc, and the response I received was “it’s crap.”
That’s an assertion, not a refutation.
That said, if a stranger showed up to my door out of the blue, and claimed the Virgin Mary had sent them to rush me off to be consecrated, you would be fully justified in questioning my mental capacity if my response was, “Let me pack my bag!”
Yet that is exactly what Thuc did when the Palmerians came for him.