"Over a billion people agree to the Nicene Creed as a basic standard of belief.
Among Catholics, there is a great deal of doctrine and a great many people who acknowledge it as true, plus many other beliefs that do not rise to the level of doctrine."
Yes, but the Nicene Creed is just part of a denomination's doctrine. The doctrine of the Roman Catholic Church contains far more than that Creed.
Take the concept of transubstantiation. While it is part of Roman Catholic doctrine, a discussion I had with two priests demonstrated to me that not even two priests shared the same understanding of transubstantiation. One believed it as a literal thing; the other a symbolic thing. They disagreed, yet both were comfortable with their priesthood.
I had a similar conversation with two Presbyterian scholars, but regarding predestination. They could not have been farther apart in their understanding of that doctrine, yet both were teaching in a Presbyterian seminary.
I did not suggest that Christians disagree with some basic parts of Christian doctrine. The devil, as they say, is in the details, and denominationalism comes from disagreement on points of doctrine which are often so small as to be almost invisible. Yet, such tiny disagreements are enough for new denominations to form, each believing that is has the true knowledge and understanding.
You are mistaken in your understanding of my "circle of friends." It's far less limited than you suspect.
Take the concept of transubstantiation. While it is part of Roman Catholic doctrine, a discussion I had with two priests demonstrated to me that not even two priests shared the same understanding of transubstantiation. One believed it as a literal thing; the other a symbolic thing. I know there are priests that are heretics. Although I don't know if you understood them correctly in this case. The bread and wine actually become the Body and Blood of Jesus Christ (that could be described as "literal") -- but it's not a molecular change (which could be described as "symbolic"). It's defined in very specific terminology and when descriptive terms are thrown around they could cause confusion for someone who doesn't already understand what's being expressed.
Doesn't change the fact that millions of people believe exactly the same doctrine as defined by the Catholic Church (same for other churches), whatever your cirle of friend or acquaintances believes.