I don't think anyone's arguing that FSoG knocks off Twilight's prose; no one has a monopoly on cruddy writing.
Well then, what is the problem? Quite frankly at this point I don't get the problem and I'm beginning to see the point her fans make about jealously. What did she knock off that is deserving of the vitriol and mocking on the net? Especially from people who haven't read it are base their assessment on hearsay or manipulated facts.
She didn't copy unique Twilight prose.
She didn't copy a unique storyline, or unique plot points, or the universe of Twilight.
The characters are comparable in some respects, countered by the vast differences. Same could be said of a huge number of books.
She didn't take advantage of the fanfic community. They got what they were promised-- a complete story for free. In fact, it's still widely available in it's fanfic version. No one was forced to purchase it.
Let's rip apart the fandom article used to support the case EL James used the fandom. The source is iffy at best. Firstly, the other party was no snow white and once planned on doing the very same thing in publishing her fanfic. The other party also left the fandom without honoring a charity commitment. Money was paid(several hundred) for a story which was left incomplete. People paid for her fanfiction and it wasn't delivered. Jealously, yep. I believe so.
In this conversation EL James said she didn't feel part of the fandom. The fandom is made up of cliques and this is a complaint I hear over and over. She wanted to prove she could write a story and then when she did she wanted to get some financial compensation for her work. Clearly that makes her a horrible, greedy person. Especially since the story was provided free to hundreds of thousands of people first and still is. And she did the work. She wrote the words. I don't think anyone can argue she didn't know how huge this would become, that it is the dream she dreamed come true.
She obviously skirted on the success of Twilight in the beginning, likewise so has everyone else whose publicist claims they are the next SM or their book is the next Twilight. Or Harry Potter for that matter or Hunger Games. No one is going to hold Twilight and 50 shades in their hands and purchase 50 shades instead. They are seeking a different audience at this point.
What we are left with is 50 shades was once a Twilight fanfic called Masters of the Universe, and wasn't written or edited very well.
My opinion on this is if the characters have a different history, situation, obstacles, emotional issues, and are a different species, they can not be the same characters regardless of what an author claims. If someone took my characters, made them human, gave them new backgrounds and wrote them into a new erotic fiction. I couldn't, in good faith, claim they were my characters or story because that is not how I wrote it.
What is created is no longer part of the universe built around the source but becomes a separate creation only inspired by the source. It would belong to the new author, not me.