I appreciate your view. However, I think the development of the trinity was a novel doctrine when it was defined at Nicaea as it lacked clear definition in Scripture. The Nestorians and Arians clearly thought so, as do the Pentecostal congregations of today.
Go in Peace
The decisions at Nicaea and Constantinople defined the doctrine of the Trinity in a way that excluded certain ranges of belief and expression that some Christians had previously thought (and continued to think) were okay, true.
But the idea was not to teach something novel, but to define the limits of Christian belief on the subject based on the Biblical and Traditional data (which, as you note, were scattered and not clear, even seemingly contradictory).
Just from the Scriptures, we have numerous data that are difficult to reconcile. Yet the Church must take all the data into consideration and ignore none of it in order to teach the truth. Heretical teachings usually emphasize one side of a difficult idea at the expense of the other, equally true side.
For example:
There is only one God.
But Scripture refers in different places to the Father, Jesus, and the Holy Spirit as being God, and yet as being distinct from each other.
When you bring in the Incarnation, also carefully defined in the Creed, it gets even stranger:
Jesus is in some places identified as God.
Yet he talks to the Father as a different person, and at one time even says “Not my will, but thine, be done.”
And it is vitally important to our understanding of the Redemption and our future glorification that Jesus was born and died a true human being, and that
one of us now reigns on the throne of the Universe.
The philosophical language hammered out at Nicaea and Constantinople is the best way the Church has yet found to embrace all of those truths simultaneously. Views thereby labeled heretical, such as “Jesus pre-existed as the greatest creation ever, but not as God” or “Jesus wasn’t really one of us, but just God in a costume” may seem simpler and easier to defend than the frankly weird doctrine of the Trinity we ended up with, but they put aside some of the data to achieve that.
Thus, in the eyes of the Church, even though “three
hypostases in one
ousia” may never have been asserted in quite that way before, the Nicene understanding of the Trinity was not a novelty but a way of reconciling and expressing truths Scripture and Tradition had insisted on for centuries already.