I assume you're familiar with the other side of this coin, right? All the pre-Christian myths and traditions that bear a "striking similarity" to the Jesus story (but came first).
We have no evidence Christians made it into Norse Territory until hundreds of years after the story of Odin on the tree.
I don't think the mythology of any of those other gods is any more ahistorical than Jesus mythology. Much of Jesus story changed after he was gone also.
Dionysius was born to a god father and mortal mother dismembered and resurrected over 1000 years before Jesus was born.