There’s lots of ambiguous information. There is no firsthand, historically agreed upon data that supports his existence in the form we know him today. In other words, there was no magical guy doing magical things.
There is no Roman record of “nailed 3 prisoners to the posts today; Bill, Roger, and Jesus the magic guy who was a pain in the ass.”
However, like Arthurian Legend, it doesn’t mean some guy like Jesus didn’t exist, or an aggregate of characters weren’t assembled to be him on story. Arthur was possibly just a chieftain of a group who fought a couple of hefty battles and made a name for himself, but he ended up being an almost magical figure with wizards and witches in the story and - guess what, he will “rise again” from the dead when needed. And no, rising from the dead isn’t owned by Christian religious figures, Osiris of Egypt did it, Dionysius of the Greek Pantheon among many others. So maybe some dude, who probably wasn’t named Jesus, caused a stir and got a few people to take note. That grew over hundreds and even thousands of years to what we have now.
Want to know why King Arthur isn’t a competitor to Jesus? He a) doesn’t offer the opportunity to control people in this life for the hope of an afterlife, b) he isn’t profitable.
An interesting thing about what we have now in Christianity though is that it basically spawned as-is in the first century, with the Gospels and Paul's letters being written decades apart, as well as Church Father's writings being very consistent. Main differences has been the Roman Catholic Church developing their own doctrine such as Purgatory over time, while the Orthodox and the Protestants tend to reject such developments.
So if it is just a legend, something must have happened to cause a consistent story to develop fairly quickly in comparison to the likes of other legends.
An interesting thing about what we have now in Christianity though is that it basically spawned as-is in the first century
The article says:
Little is fully known of Christianity in its first 150 years; sources are few.
So you’re making a huge, sweeping statement that Christianity as we know it today is based on something…we don’t know much about? There are 6 major Christian denominations, not to mention hundreds of smaller ones. Which one is the “as-is” one? The one that is exactly “as-is” from CE 100?
You're forgetting that denominations aren't actually that different. They all ascribe to the fundamental beliefs in the death and resurrection of Jesus. We do have the Acts of The Apostles as well which documents the early church. The New Testament was written within 100 years of Jesus and all Christians still follow it
But things like church structure, importance of tradition and beauty, exact liturgy formats aren't fundamental to the faith. The fundamentals stayed the same. The only real evolution was Roman Catholicism which adopted additional dogmas over time, but that's it really.
See, now you’re moving the goalposts. You made a sweeping statement that Christianity is as-is compared to the first century CE. Yet here you are breaking it down and excluding things.
Let’s just face it, you don’t mean Christianity as a whole is same as 2kyr ago. It isn’t. They held on to some facets of it, got rid of others, but kept the main themes like resurrection and the like. Heck, there are even some that suggest the resurrection story was added centuries later.