ὀρθός in the Judeo-Christian tradition is just a translation of ישר the homiletic etymology for "Israel" the yasharim (the upright). It's probably the "name" which was given to Jacob when he wrestled with the angel (hence his new name). It's the second part of the word "orthodox" which is distinctive and why I don't agree with Litwa. "Orthodox" was a brand, a brand marker like the nomina sacra. Clement knows those who call themselves "orthodox" and says they were stupid. But why is there no reference to the term "orthodox" among the ante-Nicene Church Fathers?
I'd suggest they may have attempted to consistently use the term "apostolic succession" in the place of orthodoxy. The following from the Jewish historian AM is IMO spot on:
"Apostolic succession and the doctrinal orthodoxy were pillars of the new Christian nation; its enemies were the persecutors and the heretics. Thus ecclesiastical history replaced the battles of ordinary political history by the trials inherent in resistence to persecution and heresy." (p.140)
The ecclesiastical history may be perceived to be a national history for the Christians. In the same sense it was a colonial history for the colony of Christians in the Roman empire. British colonial histories have a similar historiographical form. How the Christian nation became glorious and victorious over its adversities. The victors wrote it. The education system inculcated the future generations. It's never been revisted.
Could it be a parallel situation to what we see in Osroene where Marcionites had exclusive domain over the term "Christian" so that the Catholics were forced to use "Palutian" Christians? In other words, were the Marcionites the original "orthodox" until Nicaea? The absence of "orthodox" in Irenaeus, Tertullian, Hippolytus is astounding.
From the above we could say that these guys pushed "Apostolic succession and doctrinal orthodoxy". Apostolic succession is a pretty simple concept and can be represented in a list of bishops. Doctinal orthority might be interpeted as the oversight of the transmission history of the books of the NTC. This is similar to the preservation of the canon of Plato's books by the apostolic succession of the heads of the academy of Plato.
So the banner of apostolic succession passed through the bishop lists into the 4th century. Persecutions ceased if they existed at all) and suddenly the shoe was on the other foot. The heretical authors and preservers of the NTA became under attack. The dogma of apostolic succession became cemented in law during the Christian revolution 325-381 CE. The heretics and their books were vanquished by the lawcodes of a revised Nicene creed and trinity. (The NHL were buried).
In fact, when it comes to your theory it is "another brick in the wall" to quote Roger Waters for your ideas. If, as you suggest, that Eusebius "manufactured" Irenaeus and company in a "factory" somewhere, surely the word "orthodox" would appear everywhere in their writings (especially since Eusebius himself refers to these people as "orthodox" and the fathers of "orthodoxy" throughout his writings). Instead, we see a perplexing absence of anything resembling "orthodox" "orthodoxy" etc and instead as Litwa notes, things like "straight/correct logic/word." Another brick in the wall for your theory (not that this is about your theory, you just happened to be engaging on this topic).
I'd be inclined to suggest that the "factory" was not necessarily Eusebius but those who "preserved" Eusebius into the middle ages. This organisation was in full support of the defacto-orthodoxy of Apostolic Succession. Especially the Latin church, its popes and their officials. The "factory" included "Pseudo-Isidore of the mid 9th century. Therefore for the ante-Nicene epoch Apostolic succession and the doctrinal orthodoxy ruled. In the post-Nicene epoch the Nicene orthodoxy was established by imperial legislation.
This forced the heretics out into the light of orthodoxy. I define the heretics to have been the authors and preservers of the NT apocryphal literature. Against these guys the "Apostilic succession proponents" railed and, with a little help from the Christian emperors, prevailed.
Wearing his "orthodox" hat Irenaeus vouches for apostolic succession and the NTC. Wearing his "heresiological" hat he trashes and slanders the NTA heretics. I'd suggest that a later Latin church "factory", and not Eusebius, "manufactured" Irenaeus in the Latin language.
Engagement on this topic asks how Christian orthodoxy evolved. This is a key part of the story of Christian origins.
Even for my dabblings into the falsifying of scriptures I have to ask myself, if Eusebius "corrected" the writings of Origen why doesn't the term "orthodox" appear in his repurposings (as it does with regards to Basil's Philocalia)?
Orthodoxy was defined as the adherece to the canonical books. Heresy was defined as the adherence to the NTA books. Basil and Gregory editorship of Origen's Philocalia made readers infer that Origen --- in the
3rd century --- witnessed the NTA book of the Clementines. It turns out he didn't and that Eusebius is our first witness for the Clementines. "Correctors" (especially the Latin ones) may have operated as late as the earliest extant manuscript for Origen (or Eusebius for that matter).
Honest people are swayed by the evidence. I strive to be honest. It would seem that either Eusebius didn't falsify Origen's treatises in large part (perhaps only superficially to purge Arian statements) or he was careful to hide his treachery KNOWING that others knew that Church Fathers didn't use "orthodox"
Over the centuries they were purposefully writing and perfecting a type of colonial history for the nation of Christians in the ante-Nicene epoch and for their victory over the persecutors and heretics during the great revolution of the 4th century. Those who prepared this history were consistent in the description of the leadership of the "universal church" under the guidance of the apostolic succession of the NTC manuscript tranmission bishops. Like Origen. They rejected the NTA.
(perhaps because it belonged to Marcionism or some other group).
The Marcionites, whoever they may have been, appear to at least have the earliest inscription to "IS" the Good.
But in summary I'd reiterate that the defacto-orthodoxy described in great detail by Irenaeus, Tertullian, Hippolytus, et al, rested in the doctrine of apostolic succession back to the hypothetical door where the NTC began. And also that these guys, wearing their heresiological hats, attacked the (NTA) heretics by every means possible, including the fabrication of a false history of the NTA books.