They are young adult fiction, which is like saying that cars weren't built for driving. I'm not sure what you intend they were written as then, as they surely aren't literature.
The Harry Potter books are children’s literature. Not young adult. At least the first four or five are.
Notice how they’re almost all divided into very episodic chapters. That’s because children’s novels are generally built for reading maybe a chapter or two at a time. Maybe before bed or during reading time in a classroom.
I suspect the intended distinction is between literary fiction and genre fiction, which is a quirky socioeconomic split that seems to be particular to the realm of novels and their authors. Basically, authors of literary fiction are regarded as masters in pursuit of True Art rather than baser desires like popularity or commercial success.
Then what was it? I get that it holds a special place in peoples' hearts, but her best on offer was Azkaban and the transition from 04 to 06 is evidence that she started writing for the screen. She had a great idea. She had excellent response. She got bamboozled by billions and what could have been an English language epic became a pop culture touch point. Look at the desperate cloying for more bux via the continued franchise prequel, replete with woke characters and a-canonical bullshit. To top it off, she's one of the few people to become a billionaire and lose said status (and before anyone throws out the "muh charity" defense, her becoming less able to be generous doesn't help in the long run). HP was deligitimized by appealing to the LCD. To circle back, it obviously started as an appeal for attention; that is true of all art. But by trying to capture the world, she lost her frame, thereby relegating herself to the pop culture rubbish heap.