That's an extraordinarily weak "based on"

That is true, and intentional. It is far from obvious that the connection between the fictional Jesus and the (hypothetical?) historical one is any less tenuous than that (1) . The comparison also underscores the pointlessness of the debate : just as evidence for Vlad Dracul's existence is at best extemely weak evidence for the existence of vampires, so too is evidence for a historical Jesus at best extremely weak evidence for the truth of Christianity.

(1) Keep in mind that there are no contemporary sources that refer to him, let alone to anthing he did.