Great topic.
1. The authors are unknown, and though you could say they were trying to write history looking at the way they are written, they are also theological books.
I certainly would agree that to you, the authors are unknown, but to say they are unknown to others, would not be an accurate statement.
There are Biblical scholars who say the authors are known,
They say this based on writings of individuals living during, and shortly after the time, of writing.
There is no reason to dismiss these testimonies.
In fact, we can liken it to people throughout all history, who wrote things... "I 'so and so" did xyz".
We do not say the writers are unknown, simply because we never saw them jot down a 'letter'.
The same could happen to us, three centuries from now.
Erasing history is as easy as just saying, "No. Never happened."
Nevertheless, there is no way to determine who they were, or if they were actually writing history, and what their sources were.
Not according to scholars who do not dismiss the early church fathers, and their writings
Seems to me, persons pick and choose what they want to accept.
For example, no one denies the apostolic age, and the letters written to the congregations, but easily, many claim that the apostles wrote nothing of their leader and his activities with them.
Does that not baffle you? It baffles me.
2. a. Criterion of Embarrassment in Textual Criticism to me is acceptable. But this criterion in affirming historicity is invalid in my opinion. A reason is, you take a book, you know it is written like 40 years after an event, you dont know who wrote it, but since it has an embarrassing event that took place it is true? This could also be the flip side. Lets say something truly embarrassing is written in one of the books, and you take it as valid simply because it is "embarrassing", but did you think if the author had a "more embarrassing" occurrence that he was covering up with a "less embarrassing" story?
b. There are many movies today with lets say "Barrack Obama" speaking on the TV. Obama is a historical figure, that does not mean this movie is historical. Of course there could be a scenario where the New Testament book you refer to was written centuries later but got an ancient event exactly right and the correct discovery was only made in the 21st century (as an example), that's a whole other argument to take into consideration.
I think the first assumption can be used to create other assumptions to form such an argument.
However, these are merely argument - None of them having any structure, or foundation imo.
The first assumption is false, since the writers are not unknown... at least, outside one's mind.
So, using a number of pieces of evidence would strengthen the evidence for the reliability and authenticity of the Gospels.
1. They were known.
2. They gave objective opinions.
3. They were primary sources.
4. They are backed by secondary sources.
These are considered valid criterion, in investigation.
I consider the comic-book argument a strawman... but maybe that's just me.