If a Historian were to write a book about Churchill today
There's very throughout recordings of Churchill and his life already, even from the time he actually lived.
Also what’s so exceptional about the mere existence and death of some random itinerant preacher that would require a particularly high standard of evidence?
The entire religion formed around his person? His "wonders"? If there's such a big fuss being made about his life, then surely you'd have records of said life from when he was still alive, not very long after his death.