but not Jesus was Horus?

Yes, because I study ancient history and I know how grossly ignorant that comparison is. Zeitgeist is garbage, friend, time you let it go. Jesus was not Horus, or Dionysus/Bacchus, or Zeus, or any of that other hilariously false information which the movie plagiarized from a single woman's book, who is not a scholar, is a well known fraud, and who I (as many others have) have repeatedly torn to pieces because it's utter crap, filled with the most half-assed of half-assed research. You may as well say, 2,000 years from now, that Barrack Obama wasn't real and was based on the myths of Horus. That is as specious as the comparison.

there's no unbiased historical evidence of Jesus to start with, and even less of the "accounts" of a virgin birth, dying for sins, afterlife and miracles.

You're barely half right, and only insofar as there's no reason to believe miracle stories. But so what? By your reckoning there must have been no city of Troy and no truth in the Iliyad...until it was discovered and many of the details in the written account, unknowable by Homer's time, turned out to be accurate. Disproving myths doesn't disprove history, bub.

There is not only unbiased historical evidence, there's hostile sources, such as Tacitus. Yes, he lived decades later, yes he could have been writing what he knew Christians believed, but there is no real reason for him to pretend their claims were true if he believed they weren't as he was an apologist for Nero and loathed Christianity. There was no one happier to see Christians get shit on than Tacitus.

Most ancient historical figures have little to no direct accounts of their lives. Paul's letters concerning his meetings with Jesus' family and people who knew Jesus are better direct evidence than 99% of ancient historical figures have.

That has nothing to do with the Gospels, either, which are partially fictionalized, clearly, but with the discovery of the Pilate Stone there is confirmation of some of the claims. Dismissing most of the outlandish doesn't dismiss Yeshua's existence.

Further, the idea that there was a Jewish rabbi claiming to be the son of YHWH in the early first century CE is not only plausible, it's likely. There were Messiahs popping up all over the place, why do you discount this one and not the DOZENS of others?

Here's a hint: you're losing yourself in the weeds. It is historically irrelevant if Jesus existed. There's more direct written accounts of him than there are of Alexander the Great. Trying to "disprove" something that is not only possible, but plausible, and even likely, is idiotic. This is why these claims get laughed out by most ancient historians, because it's your desire for it to not be real so you can go "NYAH NYAH" at Christians that is overriding actual history. Which, clearly, you are not a student of.

History Channel and Zeitgeist don't make you a historian.

So they want to call themselves Christian while not believing in Christian theism.

No true scotsman, eh? They can believe whatever they like. The sole requisite to being a Christian is believing Jesus lived and died and was divinely inspired. Since you clearly know little about this period in history, or Early Church history, I would recommend you read up on Gnostic Christianity and Arianism for further demonstrations of how varied Christian beliefs can be. Simply descending from the dogma set down during the Constantinian period isn't the sole arbiter of belief, the Visigoths being an excellent example.