What is interesting is that Clement, one of the sub-apostolic fathers wrote about justification in the same terms the Reformers did, as did guys like Ambrose, and Chrysostom.
Indeed! Justification by grace through faith has always been, and will always be, Catholic. The truth of the Once for all Divine Deposit of faith is not defined by those who depart from it.
The issue is that the Church has not always been faithful to those doctrines, requiring correction.
The “Church” cannot sin, or err. Her head is Christ, and her soul is the Holy Spirit. It is these divine elements that prevent her from error, not the human. People are not always faithful, and people require constant correction, and reform. The doctrines that where infallibly preserved in the Church by the Holy Spirit did not need to be reformed.
What do you think the councils were supposed to address?
Misunderstandings and heresies. People need correction and reformation. The doctrine, which is without error, needs to be clarified when people are drifting.
Did we just get together to hang out on the Roman Emperor’s dime? Or were doctrinal corrections or declarations being made?
Maybe both?

The doctrine did not need to be corrected. People’s understanding of it is what needed to be corrected.
The reason we call it “once for all” is that nothing is added or subtracted. Corrections and declarations are not “changes” or inventions of new and different doctrines that did not exist before. For example, although the term “Trinity” was not adopted until 325 AD, it was not a new concept. It had always been the believe of the Church.
Quick, how many Catholics here don’t believe that we are justified by grace through faith? Even if you believe that this is an incomplete formulation, or that the word “faith” requires some additional definition.
If our faith did not require some additional definition, we would not need a Catechism! But it has always been odd to me that evangelicals will read Eph. 2:8-9 and stop before verse 10.
“For by grace you have been saved through faith, and this is not your own doing; it is the gift of God— 9 not the result of works, so that no one may boast. 10 For we are what he has made us, created in Christ Jesus for good works, which God prepared beforehand to be our way of life.” Eph. 2:8-10
The grace that saves us is not to be separated from the grace that produces the good works in us for which we are saved. Protestants accuse Catholics of “conflating” justification and sanctification, but for us, it is one continuous flow. One who is justified by grace through faith will move in the good works which He has prepared as our way of life.