That also deserves a serious answer.
It took 300 years to get from "the Son of God" (and that took a divine revelation to Peter) to working out a reasonably coherent (and THAT's highly debatable) Nicene theology. I don't think they had it all worked out themselves, but they probably didn't think they were following your garden-variety prophet either.
That's why I'm willing to cut others some slack.
The problem, Lambano, is that it was believed from the beginning that Jesus was God.
This was proclaimed both in the NT and also by those taught by the Apostles.
What was worked on is HOW to explain this.
Basically it HAD to come about as a response to the arians which were a heretical group.
This is the only way we can know what is heretical....
if the church does not agree with the doctrine.
Take reformed theology.
Why is it heretical?
Because it not only is not in the NT,,,,
but
the Early Fathers also did not believe God predestined anything.
It wasn't until the 5th century that Augustine brought this teaching along with his gnostic beliefs into the CC.
So, this would be a heretical teaching.
Ditto for the Trinity.