I read this with interest. But I don’t get it!
You say, “This was Luther’s breakthrough — that there is no spiritual ladder to climb. Grace is freely given at birth. We are redeemed in God because we are… here.” I’d like to see your reference for this — because I don’t think that Luther had this opinion. Luther’s point was that we can have a right relationship with God through faith and faith alone.
Luther says, “We are sinners because we are the sons of a sinner. A sinner can beget only a sinner, who is like him.” https://www.goodreads.com/quotes/598370-but-what-then-is-original-sin-according-to-the-apostle
Second, you make the point that: “when we say that ‘Christ has risen’, we don’t strictly mean the historical Jesus has risen”. What does this mean? The Bible (which is the Christian sourcebook) says in John “…but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.” Joh_20:31
Again the Bible says, ” And he said to them, “Do not be alarmed. You seek Jesus of Nazareth, who was crucified. He has risen; he is not here. See the place where they laid him.” Mar 16:6 That says to me that the Bible writers considered Jesus to have risen.
You are ever so correct to say, “Jesus didn’t live and die just to give us a new way to divide ourselves from others.” No, quite the contrary, he came as king, died for his subjects (no other religion in the world has a king like that) so that everyone can be with him. He didn’t come to judge (divide) the world:
“For this is the way God loved the world: He gave his one and only Son, so that everyone who believes in him will not perish but have eternal life. For God did not send his Son into the world to condemn the world, but that the world should be saved through him.” (Joh 3:16–17 NET.)