You say that the sin of Adam was not imputed on all of humanity: SO WHY his punishement was imputed on all of humanity, for we all die.
Even if you believe in Jesus, you STILL die, so there is no benefit in believing in Jesus.
If the matter is all about the world to come, Jesus is STILL of no benefit, as God has long since forgiven Adam's sin. Humanity has a reality. Life in this universe has a reality. And that is that all things that live will die.
That isn't a punishment. That is the way it is.
If the ultimate reward and punishment are to be found in the world to come, we still don't need Jesus.
God gave Adam and Eve the wherewithal to be forgiven. Or, are you seriously going to tell me that Adam lived for 930 years, and that in ALL THAT TIME, he had no chance to repent for his sins?
Yes, he wasn't let back into the Garden of Eden. But he prospered. He had Seth, he had a chance to see those children prosper and survive. He ate, he drank, he continued living life with his beloved wife.
I'm sure that he spoke to God many times since his expulsion from the Garden of Eden. And I'm more than sure that he was forgiven for his sins there long before his first year of existence.
But humanity was mortal. Yes, that was Adam's fault. But God's displeasure with humanity because of Adam's sins ended long before he did, I'm sure.
And human mortality doesn't change based on your belief system. Even good Christian women have pain in child birth. Even good Christian men have to earn their bread by the sweat of their brow. And all good Christians still die.
I don't really see how belief in Jesus fixes what you perceive to be Adam's sin.
God has a relationship with all of humanity, and we can overcome the wrong that we do. We have the ability to repent, and God has the capability to forgive us when we do wrong.