Infinite punishment for finite sin is unjust by definition.
Have you ever seen someone look at an old beat up car with an expression of admiration. They cared about it because they knew what it would become after they had completely restored it. They saw it as a shiny beauty when at the time it was a useless old wreck. God loved us while we were yet sinners not because we would stay that way but because he knows what we should and can become if we come to him with a sincere heart and let him clean us up and give us his righteousness in place of our completely deplorable sinfulness. If we are willing he will restore our original God likeness. Jesus endured the cross because of the joy that was set before him.
"Infinite punishment for finite sin is unjust by definition".
David, trust God. His wisdom is much greater than yours when it comes to what is just. Punishment is not meeted out time for time. Is it unjust to give a murderer a life sentence when it only took ten minutes to horribly killed someone?