I agree the quotes you picked out of Jesus predicting his death and resurrection are made up afterwards, as his followers try to rationalise what his death and failed apocalyptic prophecy might mean. It must be hard to abandon your life, family, work - everything, to follow someone preaching the end of the world as you know it, and salvation for you, that's a huge investment. The resurrection would make a different type of sense of Jesus's message for them. It's speculated other sayings of Jesus in Mathew and Luke are taken from another document (collected oral traditions) called 'Q', lost now. Either way, things like parables would be memorable and repeated I think, and the gist of sermons.It's not a lie to teach religious doctrines. The Gospels are edited by clever editors for the purpose of religious teachings to people of a time long ago. Modern needs have changed and we now need a reasonable faith that is not supernatural.
In order to fashion a reasonable faith we need the Gospels as serious literature and traditional carriers of morality. If we are to understand the life of Jesus of Nazareth we need to know what, among all the material in the Gospels, he probably said and what he probably did not say.
I'd say we can learn from the moral teachings as presented, like we can learn from anyone, without invoking 'faith'. What would it be faith in? That his moral teachings make sense or resonate with us, give life meaning and purpose? Without all the supernatural religious stuff, that's something we work out, or just live our meaning and purpose day to day, for ourselves, and are influenced by parents and all sorts of sources. It would be odd to say I have faith in Peter Singer for example, because I largely agree with his moral views and admire how he walks his talk. That's not what people mean when they say they have faith in Jesus, and it's not what the gospel writers meant. It's analogous to a retreating god of the gaps.
Right, myths and archetypes become myths and archetypes because they resonate.If the old fashioned stories help you through life they are good for you. Myths and allegories can be great and true.