Technically, once you start with the Roman general Arturias and then deduct out all of the Lancelot and Guinevere myths, neither was King Arthur "real" (although I still think there's something to be said for the Excalibur and Merlin myth-seeds, but that's a subject for another discussion).
However, some Stories need to be told.
Colonel William Ludlow does not have to be precisely "real" any more than King Arthur or Allen Quartermain, for the purpose of storytelling. It is enough that he represents the Archetype of Individuality against the stultifying constraints of Obeisance.
(And yes, I am an unrepentant Jungian, and think that Freud was a cocaine-addled fraud. We can proceed from there, if you think it important. Best, OP)
If you haven’t read Stephen Lawhead’s “Merlin/Arthur” series, you should.
It is without doubt the best example of outstanding Celtic researched fiction that’s been written.