And it took almost two centuries since then for the Church to proclaim that she is the Birth-Giver of God (Theotokos), and a Mother of God (Mater Theou).
That is presuming that no one actually spoken theologically about Mary UNTIL St. Irenaeus WROTE "Against Heresies". I think it is safe to say that he was not an innovator. His writings about the link to the beliefs of the Church and the Apostles is pretty clear. He would be the last guy I'd think was "inventing" anything.
I believe the kernel for all of our teachings were given by the Apostles, but it has taken awhile for the Church to discover herself from this one-time revelation.
Regards
This is not a presumption, Jo. It's what we know from Church history, Church documents and liturgical practices.For instance, the Liturgy of St. John Chrysostom contains numerous references to the Holy Virgin, but the Catholic Mass doesn't (I am not sure if she is even mentioned in the Mass). Thus, it is not a presumption, but what we know.
St. Irenaeus actually did bring in a novelty (c. 180 AD) when he for the first time actually identified authors of the Gospels as the Apostles Matthew, Mark, Luke and John. Up to that time, Gospels were quoted giving reference only to Christ "Our Lord said" etc. or as anonymous "memoirs" of the Apsotles (cf St. Justin the Martyr).