That is my point, brother.
Most who hold to the Theory of Penal Substitution (regardless of whether they recognize it as a theory or doctrine) work through Scripture using human reasoning. When this reasoning is different, often the conclusions are different.
That said, believe the illustration apt. Here is another:
All believe that:
1. Christ bore our sins.
2. God was pleased to crush Him.
3. The wages of sin is death.
4. The gift of God is eternal life.
5. Christ is the Propitiation for our sins.
6. The Father laid our iniquities on Christ.
7. Through Christ we escape wrath.
It is dishonest, however, to take what is common Christian belief and declare Penal Substitution Theory common Christian belief because Penal Substitution Theory is more than Scripture.
What one would have to prove is that the ECF's believed that God had to satisfy the demands of divine justice by punishing the sins of men so that men could be forgiven, so God punished Jesus in our place with the wrath set aside for our sins in order to pay our "sin debt".
While the ECF's (and all Christians) affirm 1-7, none applied the human reason of retributive justice to the equation. That is why none stated the "doctrine" of Penal Substitution (none identified what makes 1-7 Penal Substitution Theory). Instead we have the Ransom Theory, Christus Victor, Recipitulation, Satisfaction, Moral Influence, and so on.
It was not until the Reformation that 1-7 produced what is called the Penal Substitution Theory of Atonement.
It is human reasoning and not Scripture that makes the difference.
NIV Isaiah 53:5 But he was pierced for our transgressions, he was crushed for our iniquities; the punishment that brought us peace was upon him, and by his wounds we are healed.