Yep.
Some do. Some don't.
I used to think the idea of not Jesus existing was utterly wrong too, until I read Carrier's OTHOJ, and then realized how utterly paltry the evidence is. My opinion at this point is there might have been a dude named Jesus, and over time his legend grew. That's about all you can say with any real certainty.
And Jesus is a 21 on the Rank-Raglin scale.
You know Carrier is utterly in the Academic wilderness? Even his Alma Mater has denied any further connection to him. His book failed peer review, and he is roundly castigated for misrepresenting sources and ignoring evidence that doesn't fit his pet theory.
He isn't even an 'expert' in the sources. His doctorate was on natural philosophy in the Principate, so he is pontificating on someone else's field. This would be the equivalent of trusting a Nuclear Physicist about the events in 19th century Leopoldsville in the Congo, in the teeth of opposition from actual experts on Colonialism. Carrier is silly indeed.
As to Lord Raglan's scale: it was arbitrarily derived, as he himself stated, and he denied it touches the historicity of any of the discussed heroes. This is an abuse of the system, which is actually about investigating the narratives of the people in question. For instance, Alexander the Great gets a 21 if taken from the Alexander Romances or the Persian Iskander/Daras narrative, vs a 6 if we use Arrian's account. It has to do with storytelling and legend, not really history as such.
As was pointed out above, a lot of recent history would also score highly and seems incredible, yet happened.
Think of Teddy Rooseveldt being shot and finishing his speech, or he and his son trekking through the Amazon and surviving against the odds. Heroic stuff, but if this was written about someone 2000 years ago, people would make big question marks around it. It is a silly double standard that we often trust fantastical accounts from recent times, but disavow ancient ones (on average). Just because something seems beyond belief, doesn't mean it didn't happen. Truth is stranger than fiction.
The whole point of Jesus' narrative is that this is a one-time event. Augustine of Hippo already makes the point that it seems miraculous, because it is. There is also a rich tradition of reading monomyth types as prefiguration of Christ, so it really does not argue against its historicity necessarily. In fact, one can argue it confirms it, as Myth is brought into real history, a True Myth as CS Lewis says.
