Thanks for the great question!
What stands out to me is the premise on which the question is built. It seems to me that the inference is did Christ really suffered humanly and physically enough to warrant it a great sacrifice, especially in the light of His future resurrection, and in comparison to the punishment of humankind.
First of all, I do not want to make light of His sufferings. In the garden of Gethsemane, He was greatly troubled (Lk. 22:39-45) while He spent His time in prayer to the Father (the right attitude in that situation). Prior to that, He was troubled a number of times while having the last supper with His disciples, while He also chose to serve them and wash their feet (a compelling attitude when you are under pressure). I’m reading a book by Martin Hengel called Crucifixion that has been very helpful for me to better understand how dirty, humiliating and awful that cross really was. It was a literal curse word even centuries after Christ. But the most important factor may not have been the pain of the sacrifice.
The heart of the Christian message, which Paul described as the ‘word of the cross’ (λόγος το ￼ σταυρο ￼), ran counter not only to Roman political thinking, but to the whole ethos of religion in ancient times and in particular to the ideas of God held by educated people. 
Jesus acted in contrary to the expectation of a god. To the people of that time, God would not come down, yield His power, serve man, and then die for them. The humiliation in God becoming man is a powerful statement in the beginning of Christ’s sufferings, not just the incident of the cross. Instead of considering just the incident of the cross, His coming, living, and dying are all a part of His suffering and example to humankind:
John 15:12-13 NASB
 "This is My commandment, that you love one another, just as I have loved you.  Greater love has no one than this, that one lay down his life for his friends.
Beyond just an example, we can now dive into how a Jesus, God-and-man, perfect and without sin, stepped into humankind’s place as the final sacrifice for sin, coming down and experiencing separation from the Father was all to bring us back closer to God. Something He never needed to experience, but willingly did on our account. And then ultimately His resurrection speaks to the power of God to do likewise for us all.
If we look at the physical happenings of Christ, we risk ignoring the bigger, supernatural happenings of a God who was willing to lay it all down (Philip. 2:6-7). Of course, it may be hard to have a logical discussion with your colleague as the cross is simply foolishness to people (1 Cor. 1:18). But I pray that if God is drawing him to Himself, I pray his heart opens to allow the seeds you are planting to begin to take root.
Thank you for your willingness to serve as a testimony to Christ’s faithfulness. I hope any of this is helpful, or spurs more conversation.
 Martin Hengel, Crucifixion, in the Ancient World and the Folly of the Message of the Cross (Philadelphia: Fortress Press, 1977), 150.