1.) Despite wanting to sound academic and wanting to sound very informed, you don't offer a single article to a scholarly source, there's just a lot of bloviation and tirades about how there was once a Christian scholar who said X.
If you are pushing a particular niche opinion or point of view, then pointing to specific scholars who agree with you is quite important. But when talking about something for which there is absolute consensus within the academic community, then merely pointing out this fact and asking the person to take a second look is more reasonable. It really doesn't matter which source you choose; any book on Church History or the Enlightenment will do. This isn't an area in which there is any kind of controversy; the opinions are the same no matter which book you choose to pick up (assuming it's a reputable one).
Let's even agree that said scholars existed.
Wow!
Let's list the names I mentioned one more time for those who might be jumping into this discussion without having read the previous ones:
Origen of Alexandria,
St. Augustine of Hippo,
Thomas Aquinas,
John Calvin,
John Wesley,
C.S. Lewis
Anyone who knows anything at all about theology or Church history immediately recognizes those names. Furthermore, they immediately recognize the reason why those names are the ones I chose to mention. That is, because (except for C.S. Lewis) these are the luminaries of theology; the most powerful and enduring voices in the field. They are also tied to specific time periods. Origen and Augustine are tied to the patristic period (the earliest period of the Church). Aquinas is tied to the Middle Ages and the scholasticism movement. John Calvin is tied to the Protestant Reformation, and John Wesley to the Enlightenment. The people I mentioned are the key Church figures of their time; the most prominent theologians of each time period.
Saying "let's even agree that said scholars even existed" when presented with this list would be akin to saying "let's even agree that said statesmen even existed" when presented with a list containing the names: "George Washington, Abraham Lincoln, Alexander Hamilton, and FDR".
Anyone who knows anything about this topic recognizes the names and why I chose them. Pointing out the teachings of these specific scholars, being that they are the dominant voices of their time, shows that non-literal readings have been dominant throughout history, at least during the time periods I pointed to (patristic, medieval, reformation, and enlightenment). C.S. Lewis was thrown in to show the regional nature of biblical literalism (Mere Christianity is often mentioned as one of the 5 most influential theology books; the fact that within its pages, evolution is taken for granted shows the regional nature of literal readings of Genesis).
Was that the majority view amongst Christian theologians?
Yes. We've already covered this. It was.
Was that the commonly agreed upon belief of your average Christian?
That's harder to say because "your average Christian" doesn't write books on the topic.
Also, what was the quality of their disagreement, what part of the creation myth did they believe was wrong?
You are misunderstanding what it means to read something in a non-literal way.
Imagine an article about a sporting event is written which contains the words "the crowd was electrified!". Imagine that for thousands of years, people have understood that phrase in the way it was intended. It is a metaphor that helps us visualize just how loud and exuberant the crowd was. Then, imagine that a group of people appeared who read that in a literal way and promote that the only legitimate way to read that passage is to believe that an electrical current shot out, went through the crowd, and killed most people in attendance.
Now, ask the same question you just asked about the original readers. "Which portion of the story of the game did they believe was wrong?". They didn't believe any of it was wrong. They read the story of the game in the way it was intended and never imagined that some day someone would come along claiming their reading is wrong and one must read it in a literal way.