It is true that I don't atone for my sins by my own merit. But that does not entail substitution.
I am drowning in a river (the river represents death). Jesus jumps in the river, grabs me, and pulls me out. Jesus is 100% the agent of my salvation. Jesus was not my "substitute" in this scenario. Jesus does not go into the river in my place.
Our Lord Jesus did not jump in with you, he jumped in for you. The penalty of sin is eternal separation from God in the lake of fire called the second death where soul and body is cast at the great white throne judgement. God says the life of the flesh is in the blood, and the embalmer got that, and the life of God is the Spirit of Christ and of God.
Here is what God says about the man who does not have his Spirit indwelling their bodies, provided through the crucified Christ who was resurrected from the dead. Ro 8:9 But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
But if the Spirit of him (God the Father - see Ga 1:1) that raised up Jesus from the dead dwell in you, he (God the Father) that raised up Christ from the dead shall also quicken your mortal bodies by his (Christ's) Spirit that dwelleth in you.(Rom 8:11)
Jesus described the eternal abode of the damned who are paying the penalty of their own sin in the lake of fire by being bound hand and foot, having no foundation under their feet, loneliness, wandering stars, thirst, darkness, pain, hopelessness, fear, sameness, fire that symbolized the wrath of God, and forgotten of him. No one is in that place yet but this is the sentence of sinners and that is exactly what our wonderful savior, the Lord Jesus Christ, suffered for us on the cross as the substitute for all sinful mankind who had transgressed God's law, which he, Jesus our substitute, had not done.
Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.
But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed.
All we like sheep have gone astray, we have turned every one to his own way, and the LORD hath laid on him the iniquity of us all.
I am not sure how substitution can be missed.