Is following Christ truly a case of "Myth made fact" - Is Christianity, indeed, "a myth" at all?

CS Lewis's conversion, as is pretty well known, had much to do with an idea he got (mostly) from JRR Tolkien that in Christianity Myth became Fact. In other words; that various of the myths of the ancient world came true in the incarnation, life, death and resurrection of Jesus Christ. 

This is one reason why Lewis regarded Christianity as the completion of paganism (as well as of Judaism) - because in essence it took much of paganism and transformed it by the addition of specifically Christian values - in particular "Faith, Hope, and Charity".

I was greatly influenced by this idea in my own conversion to Christianity; but have now come to regard the "Christian myth" as a misleading distortion of what Jesus actually did and taught. 

My interpretation nowadays is that Christianity is in its essence about the possibility of following Jesus to resurrected eternal life in Heaven - and that this was something new under the sun: an unique possibility; that was (at its core) neither foreshadowed nor foreseen among the ancient religions: neither among Jews nor among Pagans.  

I agree with Lewis that Christianity can be and actually was (especially in the earliest years of Jesus's ministry and the early period after his ascension) an add-on, easily adopted by Jews and Roman or Greek pagans alike...

But I think the reason for this was not because Christianity was aligned with Jewish expectations of the Messiah, nor that it was a completion of Greco-Roman Paganism - but simply because Christianity was a new idea about what happened after death. 

At least initially, therefore, a new Christian convert could (and apparently did) continue to practise his previous this-worldly religion; but with the additional expectation of resurrected eternal life after death...

Instead of (for instance) dying in expectation of the underworld ghost-life of Sheol or Hades, or returning by some version of reincarnation. 

Of course, Christianity as it became, developed and accreted very large and complex mythic elements - for example about Jesus's miraculous conception and early life, and expectation of his second coming. 

So Christianity-as-is has mythical aspects with all sorts of derivations and similarities to other mythic religions. 

But I believe that this was not the case originally, as Jesus lived and taught. 

And presumably this was a major reason why people found it so very difficult to understand what Jesus was actually telling then - i.e. they could not (or would not) discard their existing myths, such as The Messiah. 

And either rejected Jesus for failing to embody the prior myth, or adapted the prior myth to fit Jesus - or else adapted what Jesus did to fit the prior myth (as with the Second Coming, notion) 

I don't know if others agree; but in the IV Gospel I see Jesus trying to tell people something very simple and clear - which they repeatedly fail to comprehend; and this, in part, because they are caught-up in already-existing religious assumptions including myths. 

After Jesus's ascension, things could have (should have, perhaps) gone in the direction of the Christian after-death expectation being added-onto various existing religions - and then modifying their content in a kind of retrospective way (as the expectation of resurrected Heavenly life worked upon the pre-existing religion).

However, this did not happen; and instead Christianity became so elaborated by mythic elements that its clear and simple essence was swamped; but also the confident expectation of being able to choose resurrection was inverted - into the necessity to submit to the judgment of God/Christ-as-King to be-fearfully-hoping to be chosen as worthy of inclusion in Heaven. 

Only in recent generations has it become conceptually and consciously possible to understand that Christianity does not need to be regarded as a true myth; but instead Jesus's work can be recognized as a cosmic transformation, a new post-mortal possibility: a Second Creation -- accessible to those who commit to following Jesus, into and beyond the transformation of resurrection.