There's widespread agreement among modern scholars that not every early Christian church had a monarchical episcopate. But Orthodox, characteristic of what he often does, has taken contradictory positions on the issue. He writes:
"And even if it [the monarchical episcopate] wasn't the earliest practice, that wouldn't refute my actual proposition, which is that it was an apostolic command that the church should have a monarchial episcopate at a later date....Firstly I didn't claim they [the apostles] did it [commanded the monarchical episcopate] later, I said that had they done it later you are not off the hook. Why might they have done it later? Because the age of the monarchial rule by the apostles was ending....There is no solid evidence for anything other than the monarchial episcopate....I'm saying nobody knows exactly how it played out, but the church witnesses that the monarchial episcopate is an apostolic teaching. Exactly what when and how that came to be is something we may not know, but that it so is what we do know....Obviously, because it [the monarchical episcopate] is the Apostolic Tradition and it is a command. It was always done this way. James in Acts is the single leader of the Jerusalem church." (sources here and here)
As those who have read much of Orthodox's material should know, he's a poor communicator, he often contradicts himself, and he frequently makes assertions without any supporting argumentation. But part of what he's saying in the comments above seems to be that the monarchical episcopate is required in all post-apostolic churches and was the form of government that existed during the time of the apostles. Orthodox argues that the apostles could have commanded that every church have a monarchical episcopate after their (the apostles') death, even if the monarchical episcopate hadn't existed everywhere during apostolic times, but he seems to think that such a scenario isn't the most likely one.
In the first thread quoted above, Orthodox also makes the following claims about Jerome:
"Jerome doesn't 'attest' to anything other than a monarchial episcopate. He gives an opinion it wasn't always so, but he gives no reason to believe he has any inside knowledge that we don't have....I've seen no evidence cited against the monarchial episcopate apart from a theory Jerome had."
So, he acknowledges that Jerome referred to something other than the monarchical episcopate existing early on, but he dismisses that view as "a theory Jerome had" without "any inside knowledge that we don't have". Yet, in the second thread cited above, Orthodox contradicts himself:
"All Jerome comments on is the naming. It doesn't help you at all."
First Orthodox claims that Jerome did acknowledge an early form of church government other than the monarchical episcopate. Then he claims that Jerome didn't do so, but instead only comments on the terminology of "presbyter" and "bishop" ("the naming").
Why would Orthodox want to change his argument? Because, as I pointed out to him, he's argued that Jerome was Eastern Orthodox and that the ancient church accepted the monarchical episcopate as something required of every church. If Jerome refers to early churches as not having a monarchical episcopate, as Orthodox originally acknowledged he does, then that raises doubts about Orthodox's claim that the ancient church always required the monarchical episcopate as something commanded by the apostles.
Before I go on to address the evidence relevant to Jerome, I should note that Jerome isn't the only patristic source who acknowledged that presbyter and bishop were originally the same office. Roger Beckwith comments:
"Other fourth-century writers, besides Jerome, who continue to recognise that bishop and presbyter were originally one, include Ambrosiaster, Chrysostom and Theodore of Mopsuestia." (Elders In Every City [Waynesboro, Georgia: Paternoster Press, 2003], n. 13 on p. 24)
Let's first look at Jerome's Letter 146. In that letter, which addresses matters of church government and whether presbyters and bishops were originally the same, he writes:
"Do you ask for proof of what I say?" (Letter 146:1)
As the Eastern Orthodox patristic scholar John McGuckin notes (see here), Jerome was arguing for something that had been largely neglected in his day. He wasn't just addressing a matter of terminology that would have been relatively uncontroversial. That's why he thinks his audience might be so skeptical of what he's saying.
Jerome goes on to comment:
"When subsequently one presbyter was chosen to preside over the rest, this was done to remedy schism and to prevent each individual from rending the church of Christ by drawing it to himself." (Letter 146:1)
Jerome tells us that what Orthodox has argued for was a "subsequent" development. And Jerome uses that reference to "subsequent" just after discussing the last apostle to die, John. He's referring to a change in church government that at least generally occurred after apostolic times.
Below are two other passages from Jerome that David King brought to my attention a number of years ago. I'm posting them as I received them from him:
"A presbyter, therefore, is the same as a bishop, and before dissensions were introduced into religion by the instigation of the devil, and it was said among the peoples, ‘I am of Paul, I am of Apollos, and I of Cephas,’ Churches were governed by a common council of presbyters; afterwards, when everyone thought that those whom he had baptised were his own, and not Christ’s, it was decreed in the whole world that one chosen out of the presbyters should be placed over the rest, and to whom all care of the Church should belong, that the seeds of schisms might be plucked up. Whosoever thinks that there is no proof from Scripture, but that this is my opinion, that a presbyter and bishop are the same, and that one is a title of age, the other of office, let him read the words of the apostle to the Philippians, saying, ‘Paul and Timotheus, servants of Christ to all the saints in Christ Jesus which are at Philippi with the bishops and deacons.’" (Commentariorum In Epistolam Ad Titum, PL 26:562-563)
"Therefore, as we have shown, among the ancients presbyters were the same as bishops; but by degrees, that the plants of dissension might be rooted up, all responsibility was transferred to one person. Therefore, as the presbyters know that it is by the custom of the Church that they are to be subject to him who is placed over them so let the bishops know that they are above presbyters rather by custom than by Divine appointment, and ought to rule the Church in common, following the example of Moses, who, when he alone had power to preside over the people Israel, chose seventy, with the assistance of whom he might judge the people. We see therefore what kind of presbyter or bishop should be ordained." (Commentariorum In Epistolam Ad Titum, PL 26:563)
Notice that Jerome tells us that the monarchical episcopate was a later development from "custom" and not a "Divine appointment". Notice, also, that above I've cited the Eastern Orthodox patristic scholar John McGuckin referring to the monarchical episcopate as a gradual development. If Eastern Orthodoxy has always recognized the monarchical episcopate as a requirement for every church by commandment of the apostles, then why would ancient sources like Jerome and modern Eastern Orthodox scholars, like John McGuckin, be unaware of that fact and even deny it?