The Church in Rome is an early Church. That is why saint saint Paul wrote a letter to the Christians in the church in Rome before he visited Rome (as a prisoner). Some one established the Church in Rome before saint Paul visited Rome. The someone was probably not saint Peter. More likely it was one who heard saint Peter's sermon recorded in The Acts of the Apostles chapter two. Possibly one who stayed in Jerusalem to learn from the Christians in Jerusalem before he/she returned home to Rome. So you are correct the Church in Rome was not the first Christian Church in the world; no one claims that it is. Nevertheless the Church in Rome started soon after the events of Acts chapter two - possibly within a year or two of those events. And since the Church in Rome is in truth a Christian Church it is in fact the body of Christ as much as any of the early churches were. Additionally the Church in Rome still continues to our day, 2000 years after it was founded. That is not so with your Protestant denomination. It didn't come into existence until the sixteenth or the seventeenth century after the beginning of the Christian era. Your denomination started to exist more than 1,500 years after the Church in Rome was founded. There are Catholic Church buildings that are 1,200 and more years older than your denomination. That sets in context the absurdity of your arguments.
More of the SILLY "the RCC is a denomination but not a denomination" absurdity.
1. Look, it is an obvious fact that there are two kinds of congregations: independent and associated, indepentant and part of a larger geo-political-economic institution. We call these non-denominational and denominational. If your parish, MC, has NO legal name shared by any larger geo-political-economic entity, no Catechism shared by any entity, acknowledges no accountability to or authority from any other geo-political-economic entity, it owns its own property, calls & ordains and supervises its own clergy, reports to nothing outside itself except directly to God - then you go to a non-denominational church. But MY Catholic parish used the word Catholic (big C) because it was PROUD to belong to the RCC geo=political-economic entity... it's property legally belonged to the local diocese of that insitutition, it's clergy was trained and ordained and now supervised by that institution, it taught the Catechism of that institution, and it was fully (and eagerly) accountable to the local bishop of that entity. Friend, IT IS NOT POSSIBLE to be more denominational than my Catholic parish was/is (and proud of it). Indeed, it considered itself FULLY intrigrated into that denomination - even considering itself founded by Jesus at Pentecost.
2. Friend, you can't have it both ways. You can't say "all parishes of the non-existent phantom are non-denominational" AND "all Catholic parishes are owned and operated by The Catholic Church (via it's local diocese), fully accountable to such, fully cooperative with such, teaching in full accord with its teachings, with clergy trained by, ordained by and supervised by that such." You can't be two opposite things at the same time. You want the RCC to be a denomination when that serves you (as in, "Don't listen to your local priest but ONLY to the Catholic Bishop" as you noted earlier today) and "The Catholic Church was founded by Jesus and has its headquarters in Rome" AND claim "all parishes are non-denominational, isolated, independent, self-contained." It's a little like saying "The United States is not a Country but it has every possible characteristic of a country and is AT LEAST as much so as any other country." It's just silly, contradictory, and nonsense. And obviously just a ploy, a "shell game" so that you can deny its a single geo-political-economic-teaching entity when that serves your purposes and the opposite when that serves your purposes. There are only two possibilities for your parish: denominational or non-denominational, either it is part of a larger institutional entity and fully associated with other parishes (and thus part of a denomination) or it not. Stop the silly contradiction.
3. The congregation in Rome was one of hundreds in the First Century. No one knows when it was founded or the names of those who did, but it certainly was not Peter or any other Apostle. It was in no sense different than any of the other hundreds of congregations except that some of them were founded by an Apostle, but not the one in Rome.
4. Peter was in MANY cities. We can confirm some definitely, but it's also LIKELY (just can't prove) he lived in Rome for awhile. Of course, he was an Apostle everywhere but he was a bishop nowhere. There is NOTHING in the historical record or in the Bible that says Peter did something SO bad that he was demoted to a bishop; in fact nowhere for centuries afterword was he ever disgraced by calling him merely a bishop. There's NO record he was ever a pastor anywhere or a bishop anywhere, but like all the Apostles, he was an Apostle EVERYWHERE - with no one certain city more or less than any other. Antioch has AT LEAST as much claim to him as Rome does - but at least they honor him as an Apostle and don't disgrace and demote him to bishop.
5. Yes, there are still congregations in Rome. Hundreds of them. Most are Catholic. It's even likely that all of them can trace some history back to the first church in that city (not founded by Peter). So what?
6. No, there is NOTHING to suggest that the Christian churches withing the city limits of Rome, Italy are "the oldest in the world." I find it more likely such would be in the Holy Lands or at least the Near East. We have several specifically mentioned in Acts (founded by some Apostle in most cases) and they likely predate any of the hundreds of churches that happen to be withing the city limits of Rome, Italy
7. There were no denominations in the First Century. In the Second and Third, Christianity was an illegal religion, mostly "underground", more a movement than a legal-geo-political-economic institution. Indeed, the very nature of being illegal made that difficult (the last thing you want is a legal list of pastors for Rome to go kill). But yes, as conditions improved, intra-congregational associations firmed up. But it was not until the Roman Empire created the Roman Church for the congregations within the geopolitical boundries of the Roman Empire (not beyond) did we clearly have a denomination (the Roman Church - of, for and by the Roman Empire). You can spiritually CLAIM that Jesus came back from heaven in 311 and founded this denomination but you have nothing in Scripture or history that remotely suggests such, anymore than the LDS's claim that Jesus did that in 1847 for that denomination. It is an ENTIRELY baseless, unscriptural, unhistorical CLAIM. Of course, soon there were 2 denominations in the Empire as a bunch of congregations were kicked out (now the Oriental Orthodox Churches) and eventually 3 when the western and eastern bishops excommunicated each other in 1054. But there was NEVER one denomination.... just for about 130 one of, for and by The Roman Empire (it never had any importance outside the Empire, where many congregations continued to be non-denominational). And then the RCC created yet another denomination when it kicked out more in 1521.
Now, what any of that has to do with the OP, I don't know.... It's just that Catholics often avoid addressing issues by parroting old, worn, wrong egotistial claims of their particular denomination... they think it "answers" everything.
.
