If you don't know what makes Jesus historical, you could just say so.
I have. Repeatedly.
I have told you that the gospels were a type of ancient historiography (certainly not the best, but not the worst), with the clear goal of reporting the past and doing so in a way consistent with biography written in and around that time (ancient historiography which was biographical differed from event-narrative historiography in that, among other things, chronology of reported events were far more flexible; that is, it didn't matter if X account really occured before Y, just that they were reported).
I have told you that however mythical the gospels appear to you or most modern readers, to those who have made a study of ancient writings they are clearly different from various types of fiction (epic, drama, fables, etc.). And even if we disregard the literary nature of our evidence and posit Jesus as some "mythic deity", then unlike every other we're dealing with one who didn't start as divine (or at least clearly divine) at all, and only began to really be considered divine by some after the gospels and much early Christian literature was written.
Also, a primary characteristic of literature intended to be fictional/mythic is the setting. Historiography differed not only by specifying the time, places, and people, but also doing so in ways which could be falsified. This is not true of mythic accounts, which take place in some distant, nebulous setting.
The amount of time which passed between the composition and distribution of the gospels and the independently corroborated information they contain, such as that on John the Baptist, Pilate, Caiaphas, Herod, etc., is found in ancient historical works, and is certainly not found in invented genres one reads about online which the gospels "really" are.
The conclusions based on the frequent comparisons between Christianity and other cults around that time, which one can find easily enough with a google search, rely on "logic" which could "prove" Wicca, Islam, and Hindu originated from the Homeric epics. They rely on summaries they distort regarding cultic practices common in the hellenistic world. Christianity developed out of an entirely different cultural and religious background, and one which operated under diametrically opposed structures, practices, and beliefs.
These oppositions existed at the most basic level. The reason Christians continue to argue over Jesus' divine nature has to do with the level of ambiguity in the texts, which meant centuries of controversy until a general resolution was reached. The entire point of myth is to
be what is needed to understand cultic practice, not confuse it. Additionally, received myth was extremely flexible, so flexible that the even the conclusions could be dramatically altered. And like other fictional genres, the flow was extremely important, because at the heart of everything from drama to allegory was a fluid story with a beginning that flowed to an end. The gospels largely consist of disparate accounts often very awkwardly joined together (which again is akin to ancient biography).
Then there is the problem of the survival of the texts and the authors that referred to them. For a great many authors and works, we only know that they exist through references from much later authors. We could pretty much reconstruct the gospels from quotations by early christians. As with any religious sect or cult, we have to ask what best explains the evidence we have. If the Jesus sect was akin to the cult of Isis or or Demeter, then we'd expect to find similar evidence. Instead, we find a set of documents completely alien to any such religious tradition, and one which originated in an entirely different culture drawing on an entirely different religious heritage.
Looking at they internal structure and development of the Jesus sect, what we find is far more consistent with types of cults/groups oriented around a central figure, all the way back to Socrates, Plato, Epicuras, etc., and continuing on to modern cult leaders than it is with any known religious group in the ancient world.
Most importantly, perhaps, we have to explain why we have the evidence we do. There are figures who are legendary and who may have existed or may not have, or who probably didn't, such as Pythagoras, Homer, Achilles, and in particular Apollonius of Tyana (a contemporary of Jesus). We also have those we know are almost certainly mythical, like Herakles. For Apollonius and Pythagoras, who are generally thought to be historical, we have almost no information until at least a century after their deaths, and for Pythagoras several centuries. Moreover, even if we ignore the late dates, include the parts which describe magic and myth, we still have less information for both than we do for Jesus. The reason that there are such problems in these cases and others like them is very much an issue of the elapsed time between the sources and the individuals.
With Jesus, we start with a contemporary who probably never met him, but who did meet with Jesus' brother James during his time with Peter. This brother is also attested to by the authors of Mark and Matthew as well as Josephus. In addition to Paul, we have an entire account of Jesus' missionary activities while contemporaries of Jesus were still around. We have three more accounts which, although not completely independent of Mark are not wholly depedent upon Mark either. Unlike almost all documents from the ancient world, these texts survived. Not only did they survive, but they did so far better than any other document, despite the fact that the religious group producing them was persecuted, and persecuted even before most of the gospels (perhaps all) were written.
We have, then, the production of several different accounts which are clearly related to historical accounts of that time, and clearly distinguishable from common forms of fictional literature. We also have internal correspondence about the dynamics of the early Christian community, which corresponds not to cultic practice/worship but to sectarian or similar religious movements which began via a historical leader. The gospels likewise are quite clear on the origin point from which the tradition they set down came, and not just the person but also the place and (quite recent) time. Moreover, they were written to preserve a tradition about the past not some set of morals or origin myths the way epic, poetry, drama, allegory, were.
Finally, apart from Josephus and Tacitus, we luckily have an amazingly clear picture of the Jesus sect development into Christianity. Not just through the gospels, or even the NT, but through those like Papias who were around and who could talk to the disciples. The author of Luke/Acts also was clearly familiar with much of the early dynamics of the church. Later epistles and non-canonical texts continue to show evolution as interpretations (beginning early with things like circumcision and later with Jesus' human vs. divine nature).
So how can we possibly explain all this (and much more I can't get into in a post) without a historical Jesus whose followers carried on a tradition which developed into Christianity? We could try to compare the Jesus sect to the followers of Mithras, but we immediately run into the problem that the few similarities between the two are either independent or more likely due to the fact that the Roman Mithras cult (the only version with any traits comparable to Jesus) wasn't around until after the gospels were already written. And with any such cult, we run into the problem of our source material/evidence: highly flexible literary compositions (usually in meter) which legitimize cultic traditions through origin stories, which were often freely adapted in fundamental ways, which do not take place in a setting like the gospels (i.e, one which can be checked out, and we have evidence from Pliny to Celsus and others that non-believers did indeed investigate), which originate out of an entirely different culture with an entirely different approach to religion than the Jesus sect, which have at their center divinity rather than requiring a 100+ development just to get to a point where a divine Jesus was a possibility, and which are fundamentally about cultic performance and sacrifice rather than theology, a set of values and teachings center to the origin figure, and which revolve around orthopraxy and structure typical cross-culturally of such cultic worship instead of a that which (like the Jesus sect) is comparable to numerous movements begun by spiritual teachers before and after Jesus' time.