I am not Catholic, but they are at least right about this: no one can read the Bible objectively or non-contextually. We all read the Bible through a particular lens. That lens is usually the lens of a particular Christian tradition or denomination that emphasizes certain distinctives. But to truly understand the NT we need to try our best to read through the lens of the first century church (to the degree that we can based on the limited information we have), and secondarily consider the writings of the church/Christians in the centuries that immediately followed since they are closest in time to the first century church and more likely to correctly understand what was intended in the NT.
@Sereni-tea posted two great videos that I highly recommend everyone watch for a balanced view on the OP vs NP debate. The speaker gives a great analogy of how he read an email from an "Emily" that they knew, but was thinking of the wrong Emily (they knew two different Emilys). The difference in interpretation of the *same worded* email was staggering all because of the contextual lens through which the email was being read.
When we read the NT through a historical first century lens (as opposed to any tradition or denominational lens) we see a distinction in the church between what the apostles proclaimed (kerygma) vs apostolic teaching (didache). The teaching (didache) is where we get most of our systematic theology, but the apostolic preaching/proclamation (kerygma) = the gospel message of salvation that was preached during evangelism/missionary efforts. That was already proclaimed and had already been believed by the time churches received Paul's letters/epistles, so we don't have a complete statement of the kergyma. But we have creeds and hymns and other statements embedded and scattered throughout the NT writings that we can extract (and scholars have).
And when we do and take a look at the apostles' actual proclamation/evangelistic preaching (kerygma) of the gospel message to NON-believers we essentially see what you already encapsulated so well for us above.
But what happens is different traditions and denominations that argue and split over specific points of teaching (didache) that were written to those who were already *believers/the church* will sometimes (often without realizing it) tack it on to the apostolic preaching (kerygma) of the gospel that was proclaimed to UN-believers and then it suddenly becomes an added condition or qualification that one must adhere to in order to be saved.
For example, and I'm not saying anyone here is doing this, but I've seen outside this forum believers who will say if you’re not teaching/including the doctrine of "justification by faith," then you're teaching "a different gospel." Now I believe in the doctrine of justification by faith, too, just as much as anyone here, and an important doctrine it is that we see in apostolic teaching (didache) sent to the churches/believers; but we never see it in the apostolic proclamation (kerygma) of the gospel. We never see the apostles preaching "justification by faith" for salvation to unbelievers *during their missionary work outside the church assembly.* That was not the gospel message that was preached, which was the message of the cross, the atoning death and resurrection and faith belief allegiance in Christ as Lord of all to the exclusion of all other false pagan gods. Christian conversion in response to the gospel message proclamation (kergyma) was not a doctrinal checklist but a personal confession and statement of Who you identified with and gave your undying devotion, loyalty, and allegiance to ("Who is your God? Ceasar? Pagan gods? or Jesus Christ?").
In very subtle ways, we tack on church teaching (didache) to the apostolic kerygma gospel message. Here are some quotes I posted a few pages back to further illustrate (apologies for my long windedness, I don't always know how best to articulate this, but hopefully the gist of what I mean (and don't mean!) is at least somewhat clarified).
"For Paul it is not the doctrine of justification that is ‘the power of God for salvation’ (Rom. 1:16), but the gospel of Jesus Christ."
"It is perfectly possible to be saved by believing in Jesus Christ without ever having heard of justification by faith."
"By “the gospel” Paul does not mean “justification by faith.” He means the announcement that the crucified and risen Jesus is Lord. To believe this message—to give believing allegiance to Jesus as Messiah and Lord—is to be justified in the present by faith (whether or not one has even heard of justification by faith). Justification by faith is a second-order doctrine: To believe it is both to have assurance (believing that one will be vindicated on the last day [Romans 5:1-5]) and to know that one belongs in the single family of God, called to share table fellowship with all other believers without distinction (Galatians 2:11-21)."
"But one is not justified by faith by believing in justification by faith, but by believing in Jesus."