@MeanMrMustard: because what you state is the view of Jesus according to Mormons (or Islam).
No, you're missing the point altogether. For Mormons the central figure is Joseph Smith. For Muslims it's Mohammad. Jesus plays secondary, if not tertiary roles. What we have here are many different denominations that say, "Jesus is the central figure. It is Him! Or him." Whatever scripture you have for your view, they explain it differently, and their view is just as sincere.
You cannot agree to reject the divinity of Christ as elaborated in the Nicene Creed and still be a Christian, it’s kind of the definition of being a Christian, ...
Well, they disagree with your definition. If you just claim your view is "kinda the definition" / defacto Christianity, then they will simply claim the same and we've gained nothing.
My point is that you may be right. They may be right. But it's not as central of an issue as your think. Or as they think. It is tiny, academic. When someone asks "what is required to gain salvation", the answer isn't the Nicene Creed. Also, the answer isn't the rejection of the Nicene Creed.
every denomination has held this since the establishment of Christianity.
So?
The trinity is just the mechanics of how God came to Earth and died for our sins in a human body, because nobody can ‘see’ God in completeness and live, therefore there must be a part of God that came down (the Son) and a connecting force (the Holy Spirit). It’s more of an explanation, but you cannot say they are separate, that would be considered heresy.
What's more important : the details of the mechanics of salvation, or the fact that there is an opportunity for salvation with pretty easy, non-intellectual requirements? Why add complication to the formula, either to require a Trinitarian God, or to reject one?
You can call your belief something else, but the majority of Christians would agree you are not a Christian if you reject that.
Except the other Christians that disagree.