Christian theology was like a puzzle made up of many unrelated pieces, like someone cutting out desired words from the New York Times and making up a paragraph and then claiming that the paragraph is from the NYT! Well, the words are but the paragraph isn't!
Eh, no. You are, of course, correct that the Church produced the New Testament scripture as a colossal feat of writing, selecting, editing, and philosophizing that spanned centuries. But it doesn't follow that the process was not inspired and even divinely dictated, or that the original pieces were not saying what they say now as a part of the whole.
There has always been the Sacred Deposit of faith that Christ left with the disciples. This gave them an internal compass: an ability to sort out the stories, reminiscences, parables, moral teaching into those that rang true and those that did not ring true. Some hypotheses, -- for example that Jesus was a ghost and not man, or that the Old Testament God was hostile to Jesus Jewish God -- were tested and found wanting. The Orthodox sense was always there; this is why St. Irenaeus may not have the entirety of the Christian theology, but those things he writes about a modern orthodox theologian could write. The councils confirmed what the Church already believed.