My observations may be biased as this is the first time I've heard of Wendy C. Ortiz or EXCAVATION, whereas I've had MY DARK VANESSA on my wishlist for some time, and even requested that my library order it (which they have, and I've reserved it).
Ortiz has not read MDV, so she's not alleging plagiarism or anything. Just noting similarities between the stories (memoir and fiction), and how the publishing world has reacted (or not) to each work.

My view: memoir and fiction are separate markets, though they may intersect.
In the Slate piece, Russell confirms that EXCAVATION was one of her many sources (50 books, maybe?) that informed the writing of MY DARK VANESSA. But also her story was partly based on her own relationships.

CW: Teenage girl/adult male "relationships". Statutory, I'm guessing.
There's been discussion about Jeanine Cummin's AMERICAN DIRT, and how maybe the story of Mexican-to-USA undocumented immigration should be told by someone Mexican or in the Mexican-diaspora.
It reminded Wendy C. Ortiz of an upcoming novel with a massive pre-publication push - Kate Elizabeth Russell's MY DARK VANESSA.

Ortiz's memoir, EXCAVATION, shares similarities with MDV. But EXCAVATION had nowhere near the mass-support: @GayTheMagazine: http://gay.medium.com/adventures-in-publishing-outside-the-gates-a06f089c372e
When seeking publication for her memoir, Ortiz acknowledges her own mistakes - signing with an agent that wasn't the right fit. Signing with a small press, when she dreamed of being with a major publisher. "And so I compromised. It was more important to me that the book existed."
Ortiz then sought to have EXCAVATION reprinted with a major publisher. Her literary agents tried, but as of now - still no.

When news of MDV came along, Ortiz notes: "The similarity of the stories, and how the book was being marketed, were too obvious to ignore."
Ortiz notes that white writers are more likely to get major publicity and support. Unfortunately, it's different for Writers Of Color.

At the time the Gay Mag piece was published, Ortiz may not have known that Russell's book was partly inspired by her own lived experiences.
"it appears that once again a white woman has written a fictional experience of a subject and publishers find it more palatable, worthy, and marketable than when a writer of color writes it from lived experience."

In this case the "subject" is Russell's own lived experience.
Ortiz's piece references this Tweet from Porochista Khakpour: "white writers who are basically ripping off their lives" - though Khakpour may not have been writing specifically about the MDV/E situation. More generally about publishing at large. http://archive.is/jbghd 
That's what Ortiz is writing about: the INDUSTRY. Which publishers and agents sign which works. Advance sizes. Publicity pushes.

I don't think Ortiz wrote this out of any malice towards Russell personally. It's the industry that's the problem. Hopefully discussions centre that.
Hopeful, but not realistic. Unfortunately, I've already seen Tweets framing Ortiz as an antagonist. People are being distracted by details (other authors, other books, other publishers), rather than the issue of THE PUBLISHING INDUSTRY PRIVILEGES WHITE WRITERS. Focus on THAT.
People are pointing out that the illustration (by Carmen Johns) that Gay Mag chose for Ortiz's piece gives off the wrong impression. I don't know what other illustrations were considered, but it doesn't represent the essay well. http://gay.medium.com/adventures-in-publishing-outside-the-gates-a06f089c372e
Some are framing the two books as being in competition. You don't have to choice between one book or the other. You can read both. Or neither. As I mentioned earlier, though some readers consume both memoir and fiction, they also have different audiences.
Primarily non-fiction readers who don't read much fiction. Primarily fiction readers who don't read much non-fiction.

Accessibility may also be an issue - format, language, price, library, in-store, online.

There's room for both books. It doesn't have to be either/or.
You know why both stories are similar? Because the authors both have lived experience of younger girl/older man relationships. And they likely aren't the only people with that lived experience. Because that's another issue that should be centred: older men in those relationships.
Key quote: "Are they similar? In as much as both young women are manipulated by predators, and write with the hindsight that comes with adulthood. A cursory googling of blurbs will lead you to believe that this is the same story published four years later. It is not."

THIS.
If people are debating what the "point" of something is (e.g. an essay), perhaps the message didn't get through clearly enough, and readers were distracted by other elements.

Everyone's reading comprehension is different, though.
Could Ortiz's points about the industry be made without mentioning Russell's book?

Yes.

Would her essay be as read by as many people if she hadn't mention MDV?

Probably not.

There were risks taken to publish this essay. You win some, you lose some.
On one hand, Ortiz is facing more negative criticism than she received before the essay's publication.

On the other hand, people are saying that after they read the essay they've ordered Ortiz's book.

These are things that writers may consider when pursuing publication.
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