The historical existence of "Socrates" and of "Jesus" are different questions -- Socrates did not perform miracles and although he had his "voices," it was only his (reportedly) telling us about them that even gives us this idea.  No public miracles, no religious teaching -- just a steady inquiry into what might constitute "the good."  Even here Socrates did not pretend to have any answer -- he seems to have mainly just poked holes into what others thought.

That we have mainly Plato's word for what the man said, and this is really all just Plato's thinking, is understood.  Still there are independent reasons to think he was real, although almost certainly not quite what Plato describes.

The main issue is because there are no extraordinary claims here, the burden of proof is much lower.