I feel like there is a point where this stops being true. That point, I think, is where it sounds like the author used a thesaurus for every other word. Like the kind of writer who refuses to use 'said' as a dialogue tag and resorts to strange, unfitting synonyms.* Sometimes simplicity works best.
I can't say I'm giving this advice from a place of having successful writing, but I have read my fair share of bad writing.
*(I'll admit that I also don't use 'said,' but I try to at least use fitting synonyms and spice up how I do dialogue tags in order for it not to sound awkward. But even still, using 'said' is not illegal. Don't overuse it, of course, but sometimes it's the word you need!)
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While I personally think having more diverse representation is important, I don't have an issue with point 8 itself. If someone comes up with a story that just so happens to not have any LGBT+, POC, etc. characters, I don't think that's a crime. Those types of stories have been and will continue to be liked if they resonate with people, even marginalized groups.
The thing I find kind of silly is the bit about fans focusing on a relationship instead of the actual story. That's... kind of how a big swath of fandom operates. It doesn't really say anything good or bad about the quality of the story or the representation. People will find a reason to ship anything. I personally find the hyperfocus on shipping a little annoying at times. I'm not looking forward to it happening to my own work (assuming it gets popular enough
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But the thing that has to be remembered is, that is a form of love. Those people liked your characters. They could've shipped two characters from some other series, or made up their own (and maybe they did), but they chose to focus on your characters.
If people only focus on one aspect of your story while seemingly ignoring the rest, it's natural to feel upset by that. Again, it doesn't mean your story has nothing else of value. People just REALLY like shipping. Considering that you described it as a GL mystery novel and not "a mystery novel that just happened to have two women in love," I imagine that relationship was fairly important to the story.