@Craig B
I think the operative word in what you wrote there is "even". There are many things that can be material and indeed spiritual too, without being necessarily biological humans. Angels and demons are a trivial example, especially at the time.
What I'm saying is that there's a subtle difference between requiring Jesus to be a physical/material being, and requiring him to be a biological human. If Paul uses "sarka" and more specifically "kata sarka" to mean "physical" or "in the physical realm", rather than referring to biological flesh, things are a lot more relaxed about what can (he imagine his) Jesus be and where can he be.
Basically what I'm getting at here is that basically if you think of a very wide material sphere around Earth, in the cosmology of the time, then the proposal of Jesus being material anywhere in that sphere isn't all THAT ludicrious any more.
And it is, in fact, what Doherty has been going on about, albeit in different words. His talking about a realm or sphere of the flesh is not wrong as such, but I think it's not the best way to get the meaning across. It can give one funny mental images. If you think of it as a
material realm, or
physical realm, things are IMHO clearer.
And in fact, that's the whole mythicist hypothesis in a nutshell. (As I was saying, I'm not taking it as more than a hypothesis.) You still have a material/physical Jesus, who took the outward appearance of a man, and who became the spiritual successor of David in the material realm. It's just as material as HJ, really. It just isn't exactly on Earth. You can think of it as being on a secret moon base or on Planet X, in modern SF terms, but in middle platonic terms it just was in a higher sphere of the real world.
Edit: and granted, it may still seem crazier to make up an astronaut Jesus than a human Jesus. But they weren't making up either, they were making up a superman Jesus. In which case whether he's from Earth or Krypton is just backstory details. And religions have gone farther off the deep end than that before. Plus, considering that Paul shows textbook syndromes of paranoid schizophrenia, and takes his lore from halucinations... yeah, I don't think something being crazy is much of a counter-argument in Paul's case