At best, we’ve all read a bad translation—a translation of translations of translations of hand-copied copies of copies of copies of copies, and on and on, hundreds of times.

You might as well argue no one has read the Illiad.

So where does the clear declaration of God and Jesus as part of a triumvirate appear in the Greek manuscripts?

The argument for the Trinity is based on the opening versus of John's Gospel. "In the beginning was the Word and the Word was God and the Word was with God." Jesus is considered the Word (Logos) Incarnate. This idea seems rooted in ideas Philo of Alexandria had though Christianity does expand it. John's Gospel does seem to refer back Philo's ideas. If you start with Philo's ideas and then read it, it starts making a little more sense.

There are some translations of the bible that seem to deny the Trinity by adding "the Word was a God", but this is an issue of languages differing and translations being an interpretative art form.

Certainly there being some ambiguity within the scriptures led to there being a divide in Christianity. Hence the council of Nicea. This was a counsel of bishops. Viewing Constantine as ultimately making the decision is a very Protestant interpretation of the events and stems from the old Protestant anti-Catholicism.

I mean, realize in reading this news article you are reading an interpretation of an interpretation and not all the sources being used are being cited. This is actually more filtering of history than what you are claiming the bible is doing.

History is simply story. The historical critical approach likes to remove the fantastic elements of previous histories as they were recorded and come up with a new "realistic" story. "Here's what really happened." It's an approach, but it's not the same as a time machine. We are still left with a mere story.