The whole question of whether there was an historical, real living person who gave rise to the Mythical Literary Figure we are presented with in the Gospels is simply a matter of mild academic interest, it makes no difference, one way or the other.
Let's just assume there was an itinerant, rabble-rousing, Jewish political activist man who the Writer of "Mark" based his Character upon, that does not make anything else at all, not one thing, in the Story true.
Just as an example take the literary character Sherlock Holmes, we are quite sure that Conan Doyle based Holmes on a man who taught him, but that does not make Holmes and the Stories true, and it does not make any other character in the stories true either !
So, Dr. Watson, Moriarty, and Mrs Hudson et al are no more real than Holmes himself.
And neither are the other characters in the Gospels !
The Apostles, disciples, villains etc. we find in the Gospels are as imaginary as is the Jesus figure.