Writing skills can do you well, for fantasy.
But when what you're writing is a mystery, other skills are necessary. Word flow is not enough. You need feelings of "mystery" in the mystery novel.
And sadly, once you know Rowling, you sort of know where all of her characters are going. You do not even need to know that it is Rowling writing (as I did not), because once you realise that the first 10 of her characters have been obnoxiously, tediously 2D cardboard caricatures, you start to expect that the 11th character will be the same.
And you will be right.
Is it always a problem if characters "fit a mold"? No. In fantasy like Harry Potter, stereotyping is great. Morphing "white rich racists" into "anti-muggle Death Eaters" works fine as a narrative device to expose bigotry. Nobody is surprised that they are up to no good, since they aren't meant to be a surprise. They're Death Eaters. It's in the name.
When Dumbledore turns out to be gay, that is a delight, because it is a surprise, but one that makes good, retrospective sense to the story, and doesn't feel forced. And even if you knew, nothing hinged on your not being able to guess it.
But a mystery doesn't work that way. Nope.
When suspense depends on you not being able to guess that the killer is the rich white male acting on sublimated racial hostility (spoiler alert... but, we knew it already, right?), when you can guess that the black security guard proves to be a decent, hard-working sort whose intelligence is underestimated by nasty white people - unlike his sniveling, greedy white counterpart, who is (you already know...) going to prove to be a nasty little liar - that the spunky female protagonist has a boring, unsexy, wimpy husband who is going to prove to be "unsupportive" of her career, unlike the sexy, tough, big bad boy protagonist who respects and desires her, etc etc... everything starts to look like a cookie cutter, spawned from the mind of a certain kind of white liberal female who has never been in a street fight, and talks patronisingly to minorities all the time.
This isn't so bad in Harry Potter, because it's fantasy. But in a murder mystery thriller based on cringeworthy racial subtext (...egh), you sort of know where things are going by page 30, as far as the "mystery" goes.
And then, it's not a mystery.
You find yourself clinging to a hope that you are wrong, and that Rowling has been cleverly snookering you into thinking she's predictable and preachy, while in reality she is deftly playing on your prejudice.
But, no. She's just that simple.
Nobody is supposed to have known that it was Rowling who wrote this book, under a pseudonym. But, this book IMHO would not have gotten far without being Rowling's book, word must have gotten out. It's just too stupid.
Stick to Death Eaters, Rowling.