These aren't really easily distinguishable. Certainly the popular understanding of just about any figure won't actually fit well with that of historians.
You should think about why we have sources on everyone else that we have sources on. Sources exist for a reason. People that enter the historical record do so because of a specific reason. That will always have an effect on our ability to piece our understanding of them together. You're drawing a sharp divide between religious figures and other historical figures that doesn't end up working particularly well.
Oh I know how difficult it is to actually know about people from long ago, and that the difference between Alexander the Great and Jesus is probably semantic; but that's why I asked if it mattered.
I guess another way to look at the question is should we allow somebody who may very well have not existed at all if enough people believe that person existed? At one what point should we draw a distinction between historical figure or religious/fictional figure? Or should the line be there at all?
It's possible that my perspective is just wrong. I don't know. There just seems to be a difference between somebody who we think we know a decent bit about their life, like Julius Caesar, and somebody like Jesus who we have sparse information on the man we believe is Jesus but little evidence that backs up a lot of what most people would say happened in his life.
To pose a crude metaphor, in Iron Man 3 an actor played the role of the Mandarin. If 1,000 years later 35% of people in the world believed the fictional version of the character was actually the real person and scholars could only agree that the guy existed and a few other events while the majority of his life was hotly contested, how would he fit in the debate?
I'm totally being pedantic and I do apologize for that.