I don't "propose" any particular dates or anything about "stabilizing" anything.
My bad. I made the assumption that when you stress that the texts of the gospels that we know about are from 4th-6th centuries, that they orginated from shorter oral tradition going back to centuries BC, and that the existing fragments don't tell us anything about the contents of the gospels at the time the manuscripts were written, you would also think the contents have changed. But again, scholars have identified that Isaiah was written over two centuries by analysing its text. If something like that happened to gospels, too, there should be evidence in the surviving text for that.
Why do I "need to be able to explain its existence if you want to propose that Luke was written centuries after Jesus"? I have said not a word about the date when g-Luke may have been first written down.
You have said that we can't know whether the text of Luke that we have is different from the original text. And I'm saying that the affair of Marcion pushes the date for complete Luke from the 4th-6th century that you stress so strongly to the early 3rd century the latest. That, or you do a full dejudge and claim that Tertullian's writings are forged. (If he hasn't claimed that yet, he will claim so in the response to this post since Tertullian claims that Marcion used Pauline epistles as source, and Marcion wrote before that magical AD 180).
In short, there are two options for Luke:
* Tertullian had essentially the current Luke in the early 3rd century.
* Tertullian's
Against Marcion is a later forgery.
Tertullian's writing also provides evidence that Luke was already existing in 140 as he claims that Marcion modified it.
What I said about it is that figures like Pythagoras are known for, and historically important for, the entirely factual human things associated with their names. E.g. the discovery of a mathematical theorem or the presentation of a philosophical idea, etc.
You do know that the first source that we know of that explicitly connects Pythagoras with the theorem comes from the first century AD, don't you? Half a millennium after his death. The oldest extant manuscripts for that come from the 10th century. Well, earliest extant manuscripts containing parts of
Morals of Plutarch, I don't know whether they contain the parts mentioning the theorem. Plutarch also tells us that Pythagoras had a golden thigh, which isn't too common feature among entirely factual human beings around where I live.
As a tangential digression, I checked again to see what the earliest source about Pythagoras says about him. Not much. Herodotus says that "he was not the least philosopher" and that Greeks living around the Black Sea tell hos former slave was worshipped by the Getai as a major god. Which is surprisingly quick development, given that Herodotus was born about 10 years after Pythagoras died. Herodotus writes that he himself didn't believe the tale of the slave, but it's still impressive that less than 50 years after Pythagoras's death he had a large enough fame that some people were willing to believe that his
slave would have enough magical mojo to establish himself as a god among barbarians. The specific feat that the slave supposedly did was to live for three years buried underground before emerging alive. Hmm... someone being buried for three something something and then emerging from the grave. Sounds curiously familiar, I wonder where I have heard something like that before.
Jesus in stark comparison is famous purely and entirely for the claimed string of constant miracles. He is not famous for anything else except the supernatural and the prophetically divine sayings attributed to him. He is not known for any factual remains at all.
The sayings attributed to Jesus include things that aren't particularly prophetic, for example, stuff like ethical teachings. You don't need to be a god to say these. You don't even have to be a god to say that our generation will see the coming of the kingdom of god. Or else I walked past two gods today when coming home from work. Not to mention that it would take a great amount of boneheadedness to put a prophesy that's already failed into the mouth of an invented god-man. The kingdom of god didn't come before Jesus's generation was gone. But, Jesus-mythers insist that early Christians were that bone-headed.
In short:
* both Pythagoras and Jesus were sons of gods and have also other supernatural things attributed to them.
* both Pythagoras and Jesus have humanely possible things attributed to them.
* neither left any physical evidence for their existence.
* neither is mentioned in surviving contemporary texts.
* both had followers who founded new religions based on their teachings.
* and, the thing that you for some reason hold critically important: no writer ever claimed to meet either one in person.
Goose. Gander.
Whereas in the case of Jesus, completely unlike Pythagoras or Caesar or any of the others, it is the existence of Jesus himself which is absolutely crucial and essential to the existence of Christianity today
The existence of Christianity today is completely irrelevant to the question whether historical Jesus existed or not. It doesn't matter the slightest bit. And conversely, the nature of Jesus is mostly irrelevant to the actual practice of Christianity today.
... but if Jesus did not exist, then Christianity is certainly rendered invalid and based upon pure fiction.
And an existing Jesus who got executed and didn't raise from the grave renders Christianity just as invalid.