I am confused - you state - "As a human, Jesus' atonement could have been for one man but not all men."
According to the Law of Moses, Jesus was executed, his death was not a sacrifice according to the law which prohibited human sacrifice. But going outside of the law what is a human life worth? What was Paul's life worth? With regard to sin Paul was without condemnation, did his death provide atonement for mankind?
Because of his past, Jesus' life was worth more than the lives of everyone in heaven and on earth. There was not anything made that Christ didn't make. He is the Creator. The Creator died for his creation at the behest of the Father. However, he recovered nicely and all is well.