I disagree that the Nicean Council decided on what was the orthodoxy; they merely agreed on what was already accepted as the orthodoxy for several hundred years. Their only quibbles were over a couple of minor books of little importance relative to the others. The Eastern Churches, the Western Church, and the Coptics/Egyptian Churches all kept their respective selections of books; the variations were very small. People with ulterior motives keep trying to make huge mountains out of that for some reason, usually not at all good ones.
Certainly the issue must have been picayune and immaterial to outsiders, but Christians - at least those who participated in the debate - deemed it rather important. Especially the priest Arius and his bishop Alexander.
Alexander won more support than Arius did, and Christ's equality with God was one result of the Nicaean Council.
Constantine called the meeting for a variety of reasons, as you say, but this was one of them.