What we have is plenty to say there was a historical Jesus (named Yeshua but whatever). There was nothing written contemporaneously about any of the illiterate builders and fishermen in the region, one became important enough that non-illiterate people started writing about him pretty soon after.

Paul's Epistle to the Galatians was probably written in the year 48, only 15ish years after Jesus died. Paul never met Jesus but it proves there were people talking about him pretty early. And he talks about meeting James the brother of Jesus in a later letter, and James' execution was mentioned by Josephus in the year 94, Josephus being a non-Christian corroboration 30ish years after the fact.

People can make the case, but people can make the case that Constantine didn't exist too. We only have so much corroboration possible so far back in history.

As for PARTS being fictional, haha yeah. Jesus only says he's God in John, the last gospel. Pretty big thing to forget to mention for the earlier 3. Plus many stories between gospels that conflict or at least get changed which is a weird thing to happen if both stories are literally true. And that's not to mention the conflicting Genesis stories etc.