Nice theory but it does not work. There were bishops who lived, and gave their lives for Christ, before Constantine. The writings of the pre-Constantinian church Fathers show that they were Catholic. The theory of the Constantinian origins of the Catholic Church also does not work because one would have to believe that the church survived 300 years of brutal persecution only to be crushed by Constantine without a single word of objection. Sorry, that does not work.
Of course the errors of the Catholic Church were begun before Constantine. Paul spoke of many of them and John revealed in Revelation some of them. It wasn't crushed by Constantine. The Catholic Church errors were just expanded, accepted, and spread under and after Constantine. Constantine was just the facilitator of the expansion of error.
You are assuming I believe Constantine was a light switch, the pre-Constantine church one thing, the post-Constantine church suddenly something altogether other. I do not see it like that. I see the pre-Constantine church morphing into the Constantine one, the Papacy years later putting the finishing touches to the “morphing” process.
You assume the pre-Constantine ECF bishops are equivalent to the original church in the book of Acts. Acts 20:29, 30 would say otherwise. It proves it doesn’t take several hundred years for people to backslide from original truths: after Paul’s departing Ephesus, grievous wolves would enter in among them, of their own selves men would arise speaking perverse things to draw away disciples after them.
I see the Papacy representing the worst form of the “grievous wolves speaking perverse things” trend Paul warned about.
Main line Protestantism is more representative of the ECF. True Christians are more Berean than main line Protestants, going further in measuring Christian beliefs against the NT.
The Papacy? It is so far out in the Constantine-Roman-pagan weeds, it is not even funny, not even relevant.