The doctrines relating to Mary came later because the challenges to the person of Jesus came later. Was He truly Man and truly God? All of the Marian doctrines are directly related to the truth of Jesus as the Christ and as the second person of the Holy Trinity.
Yes, the title Mother of God, was a bad decision by the church. It was a title created to emphasize the Deity of Christ, NOT Mary's position. It has led to heretical beliefs the early church DID NOT believe in and continued to be unknown for hundreds of years after the resurrection.
I don’t agree, obviously.
The Trinity, as we know it today, was unknown for years after the resurrection, but the Truth of it existed hundreds of years before it was known.
The Apostles never taught it, nor did they even try to explain it. We have no clear idea of what or how the Apostles thought regarding the Trinity, but we can find the Truth hidden in Scripture.
Hundreds of years after the resurrection, there are those who deny the Trinity, who do not know this truth. Does that mean that it is heretical since we cannot find any explicit teachings on it in the NT?