I think a weakness of this "first hint, whoa, the third century, must be an innovation!" reaction is the assumption that if the first writings we have in print are from 250 AD, it must have been invented by the writer in 250 AD.
That is dubious on the face of it. Consider that the term "Trinity" wasn't used until about that time ---- mid-third century, Tertullian --- and the term "Incarnation" with its precise definition wasn't hammered out officially until 100 years after that, at Nicaea, and was still being refined as late as the Council of Chalcedon in 451.
The art and inscriptions concerning Mary found in the Catacombs of Priscilla date, as well, from the mid-third century They show what the Christian martyrs in the Coliseum held dear and certain, what they were willing to die for. This tells us, not only Christian doctrine, but Christian culture.
It would be foolish to say that the earliest Christians did not, on the basis of Apostolic testimony, believe in the Trinity or in the Incarnation. As you surely know, the spark-plugs of conflict and controversy are historically instrumental in getting the engine of definition and doctrine moving: one does not define a commonly-accepted doctrine with elaborate precision unless somebody has been challenging or denying it. The challenger raises his arguments, and then the Church is forced by the crisis of the situation to refine its terms to defend the Truth which was first received centuries earlier, and preserve the Unity of the Church.
Second, Origin was writing at a time of blistering controversy, in which anything that seemed dicey would have been grist for the polemical mill. If anybody thought "Panagia" was heretical, I'm sure Jerome, Ambrose, Eusebius, Demetrius of Alexandria, or any of his other Alexandrian or Cappadocian critics would have blown the whistle on him. But they didn't.
This is not the say that everything Origen wrote was orthodox. Not at all. It IS to say that we can get a pretty good idea of what was serenely received as unexceptionable, and what was not. A sheer innovation would never have been considered "unexceptionable" if it created some sort of interference pattern with the sensus fidelium (if you will permit me a physics analogy) -- not when there were so many there to debate it.
Regarding Mary....were all of the ECFs in 100% agreement in their writings on Mary?
What your so called “early Christians” did is immaterial. Already in Paul’s day we see “Chrrlistians” going off track where he chastized them and corrected them.