What is it you do not understand? 
Arius said Christ was fully human.
Many said Christ was fully divine.
Some said a mix of human and divine.
All but Arius affirmed that Christ was divine, and was human, that this was the faith they had brought with them and that they recognized in the Creed.

 “More than three hundred bishops, remarkable for their moderation and intellectual keenness, were unanimous in their confirmation of one and the same faith, a faith which has arisen in agreement with the truths of the Law of God. Arius alone had been misled by the devil...” as Constantine put it. 
I do not see how you can use that history as an example of “objective truth tells us both cannot be right.” It was not side A versus side B, and B changed to agree with A, as you would have it. It was 300+ bishops, with 300+ opinions, who each saw their faith reflected in the one creed.
If you see it differently, I’d love to hear how.