Great question I think it helps us to anchor our faith in God’s plan more firmly, and it encourages us to trust in the Lord, that Jesus, the God Man is the only way for people to be saved.
As I read your question it seems settled that Jesus is both God and Man, but the question is; does he have to be God and Man, and why does He need to have two natures within the one person Jesus.
As I think about your question I go back to Genesis 3 and the fall of people. Paul sums up the results of Adams sin well in Romans 5:12-21. Because of Adam’s desire to determine for himself what is good and evil and the power of the sin nature within all people; if Jesus was just a man he would not be able to save himself little own everybody else. It is only with the power of God that people can rise above the power of sin in people lives. This power is what allowed Jesus to live without sin. Therefore it is only with the power of God that He could be the spotless lamb. I think that we should also remember that Jesus temptations were very real….just like any man. Matthew 4:1-11, but He overcame them by the power of the Word. We are so fortunate that when we turn and follow Christ we also get the same power and resources to overcome our temptations as well.
The next thought that comes to mind is that the punishment for any crime is somewhat dependent upon who the victim of the crime is. If I slap the face of my neighbor I will get one sentence but if I slap the face of the arresting officer, I will get a steeper sentence, and then again if I slap the face of the presiding judge my penalty for the crime will continue to escalate. All of our sins are not only against those we journey through life with but they are also against the most special, sacred, all powerful God of the universe. The one that we owe our very existence to. Thus even our own lives don’t have enough value in them to repay the debt that we owe to this omnipotent being. Therefore something of greater value than a human life, something of the value equal to the one that has been wronged must be part of the justification process in order for the punishment to fit the crime….remembering that our God is completely just in His judgments.
Looks like you have many good thoughts on this subject already, maybe there might be something else here as well to benefit in your discussions.