ukpimo: So you're saying there is an off chance that someone could be believable, but only if we actually lived at the time that person lived?
I'm saying that it is reasonable to accept that a person existed at a particular time in history, as so many people have. And it is reasonable to accept that they did things a normal person could do, like give speeches and promote charity and experience mistreatment or even death at the hands of their enemies. Even if we don't know any of this for sure, it's not outside of the norm. It happens all the time. It happens today.
If we say that a person who existed also performed miracles, or was assigned a task by an angel, or by a deity... these are not things that happen frequently. They may not even happen at all. Even when we cannot determine for certain that a person existed in the past (due to the lack of evidence in the archeological record), we can accept that they probably did. And we can accept some claims at face value, if they describe actions that are not out of the ordinary.
Because the evidence is so sparse, claims that any historical figure did extraordinary things must be met with skepticism, and two reasons come to mind: for one, as the evidence for past figures becomes more reliable, such claims conveniently begin to dry up. Two, people will accept such claims for one figure, but reject those claims for all others. This isn't based on a specific and unbiased approach, but on what the person already believes, which is a bad way to approach evidence.