I just realized a few minutes ago that I wasn't being fair in my comparison of the Book of Mormon to the other 2 books I listed. Breaking Dawn is only one volume in a 4-volume series, and there are 3 books in the Lord of the Rings Trilogy. Both of those books are just one piece of a larger body of work. So I'm going to correct my numbers here to give a more accurate comparison.
There are approximately 560,000 words in the 4 books in the Twilight Saga. It took Meyer about 5 years to write them all. And there are about 561,000 words in the Lord of the Rings trilogy and it took Tolkien 12 years to write it. Of course, all of these numbers are just estimates, but since the same method was used to calculate each of them, I think it's a useful comparison.
So, both of those books are about 2 1/2 times larger than the Book of Mormon is when put into perspective.
Another example I just thought of is Harry Potter. J. K. Rowling wrote the 7 books in that series in about 17 years and together, they are approximately 1 million words. Okay, so THAT is a big book. :D Rowling was about 47 when the last Harry Potter book was published, and was also a college graduate.
Like I said, nothing is impossible and there is no absolute scientific proof one way or the other that is going to say if the book is an historical record or a work of fiction. Joseph could have just been an amazing writer, up there with the likes of the best fiction writers of the 20th century.
But the other thing we have to consider is that these writers didn't just take up a pen one day and decide to write a book and get it right their first try. They worked and practiced the craft for a long time before coming up with the story and writing it. Rowling said she wrote almost consistently from the age of 6. That means she practiced the craft of writing stories for 20 years before starting to write Harry Potter.
Tolkien, in turn, wrote scholarly publications, as well as other kinds of articles. He also practiced his craft by writing editions and translations of Middle English works, he studied languages, and he practiced the art of storytelling for years before actually publishing any works of fiction.
Just by virtue of graduating with a degree in English, Meyer had to have practiced the art of writing as well. A lot.
And I do have to sneak in one more correction here on the subject of education. I had said in my last post that he had the education of a modern-day 4th grader. I was thinking about it and it didn't sound right, so I looked it up. He actually had only 3 years of formal schooling. That would make him more like the level of an early-1800's 4th grader if anything, which is a much different thing altogether. He was mostly schooled at home and spent most of his time working in the fields.
If we look at The Book of Mormon as a work of fiction, it is an amazing one. It is an epic saga unlike anything that has ever been attempted before. Characters and storylines flow into each other and cover a huge amount of time. There are no plot holes. Different characters write in different styles. Some of the stories are told in 1st person. ("I, Nephi, having been born" and "I, Moroni, after having made an end" and "I am called Mormon" for example) and others are told in 3rd person ("And it came to pass that Alma and his brethren" and "Now Ammon said unto him" and "Then Jared said unto his brother") During the chapters that are in 3rd person, Moroni interjects his thoughts here and there. During the chapters that are in 1st person, he doesn't. When Mormon is abridging the plates, there are places where he quotes the person he is writing about ("Alma began to deliver the word of God . . . saying, I, Alma"), but when he's done quoting, he goes back to 3rd person. Nowhere does it vary. That is a lot to keep track of.
If we look at The Book of Mormon as a work of non-fiction, it is also amazing. (We do have to look at it as a work of non-fiction even if we think Joseph Smith wrote it instead of translating it, because he marketed it as such and it is set in real places and a real time period in the past.) There are so many details in the book that would have taken a lot of research to get right. What is the terrain around Jerusalem like? How would middle-eastern people have acted? How do you prune olive trees?
If we look at the Book of Mormon as a piece of falsified scripture, it is also pretty darn amazing. It's one thing to study the Bible voraciously, but it's quite another thing to write in that language in a way that mimics real scripture.
But, on top of all that, if Joseph Smith did write the Book of Mormon, he would have had to do all three. He had to have been amazingly good at mimicking scriptural language, as well as being a master at fiction-writing, and he had to have also been very good at writing non-fiction as well.
Considering the time frame he wrote it in, his writing experience, the scope of the work, his accuracy in details that it takes modern-day writers tons of research to get right and a group of editors to perfect, I just personally think it is extremely hard to believe that he was that good. Like I said, though, not impossible.