Just where do you think “they” got the idea of a Trinity to be able to formally define it? You are simply ignoring the clear Scripture that WAS the basis for the doctrine. If the Apostles didn’t believe that way, then why did they teach about it in their letters to the churches??? You look at some passages and add your OWN theory but you ignore way too much that disproves it.
There is not clear scripture to support a trinity. That is why it took over 300 years for traditional Christianity to accept it. Scripture is clear that biblical figures believed in a God that composed of the Lord Jesus and his Father. John 1:1-2 is clear about this. ALL glimpses of God's throne in heaven in scripture do NOT show, mention or hint of another entity called "the holy spirit" comprising the Godhead.