I think we have to keep in mind that theological development always addresses the contemporary. What I mean by this is that theology tries to answer the questions being asked.Indeed! And at such a cost.
The reason I do not tend to use the term 'sin debt' is partly because of the rabbit-hole down which we are now diving.The debt that we owe God is not money. Yet the analogy of money is used in the Bible, most notably in the Parable of the Unmerciful Servant and in the Lord's Prayer. Men are morally and spiritually bankrupt before God; they owe God perfect righteousness (Leviticus 18:5; James 2:10) but they are unable to fulfill their obligation (Romans 3:10) and therefore come under the righteous anger (wrath) and condemnation of God (Psalm 7:11). Christ is our 'surety' or guarantor (Hebrews 7:22). As various verses in Proverbs show, a surety is responsible to take on the entire debt of those for whom he is the surety, and that the Lord Jesus has done.
SFAIK, there are no books on the atonement before Anselm. When we look at the ECFs we are looking at comments made as parts of other arguments.. For example, we read from Irenaeuas, 'The Lord redeemed us by his blood and gave his life for our life, his flesh for our flesh, and poured out the Spirit of the father to unite us and reconcile God and man......' [Against Heresies, v.i. 1-2] It's pretty thin, but it certainly doesn't deny Penal Substitution, but it's just a tiny part of Irenaeus' great argument with the Gnostics. P.S. doesn't really concern him.
My own experience has been that when I was saved at the age of 38, I knew no doctrine, and the church at which I was converted was pretty doctrine-lite. It wasn't until a few years later when I began to study that I came across the various doctrines concerning the Atonement and Penal Substitution appeared as the only consistent one. However, it is discussion on this board that has really made me search the Scriptures and firmed me up on the doctrine, so to that extent, I owe you my thanks.
I have to finish now as I'm off to a meeting.
People have argued, for example, that John Calvin did not hold to the doctrine of limited atonement. Technically, this is probably true. BUT the reason is not that Calvin rejected limited atonement either. The reason is that the issue of the scope of the Atonement was a post-Calvin issue.
It is a fact that no one prior to the Reformation held what is known today as the Theory of Penal Substitution. BUT that does not necessarily mean that those who held the elements advocates point to in ECF writings (both penal and substitutionary aspects have always been inherent in the Atonement) wouldn’t have affirmed the Theory had they been contemporary to our time.
You often turn to Trinitarian doctrines as an example of theory vs. doctrine. It is a good example here. The doctrine was developed over time. Does this mean that the Apostles would have rejected the Doctrine of the Trinity? No. But at the same time they did not affirm the Doctrine in the way that it became articulated (three coeternal hypostases; the relationship of perichoresis, eternal generation, etc.).
So looking back at what the Church believed prior to the Reformation really doesn’t prove or disprove the Theory of Penal Substitution. Was the basis of redemption, in their minds, God punishing sin by pouring His wrath upon Christ who took our punishment in our stead? Only if we ignore context and replace “them” with “us”. But they also did not think in the same terms as us. They were not subject to the same ideas, the same philosophies, and the same ideologies as the post-Enlightenment world. They had a different worldview. The contemporary questions their theologies addressed were not exactly the same contemporary questions we would address. We can say (without doubt) that they did not hold Penal Substitution Theory, but we cannot say that they would not have (or that this proves the Theory incorrect).
Which brings us back to Scripture and the necessity to first examine and prove our presuppositions (not only yours, but mine as well). In terms of Penal Substitution Theory it is up to you (to those who would defend the theory), not me (or those who oppose the theory), to make a case for retributive justice as divine justice. Likewise, when I defend my position it is up to me to justify those things that I would presuppose.
The reason I believe this to be true is that IF redemption is based on divine justice AND divine justice is retributive justice, then I see no logical disagreement with the Theory of Penal Substitution. If the presuppositions the Theory hold are correct, then there exists no grounds for disagreeing with the Theory because it is the only theory that addresses the Atonement in that context. So if I held to the Theory, my first priority would be to prove its presuppositions. If they are proven true then the argument is won.