I think the author's ability to help the reader suspend disbelief is important and that reader's will overlook "bad writing" if the over all story is good. The actual language used by an author can pull the reader out of the story. If sentences are awkward or dialog stilted that will distract the mind's eye causing the audience to focus on the actual device (words) as opposed to the story. When that happens readers may dismiss an author as a "bad" writer.
Good stories need to be "realistic" enough that the audience can suspend disbelief; even in fantasy or science fiction. Even the hidden magic world of Harry Potter followed conventional "muggle" rules. 805
There was the typical governing bureaucracy, kids still had to go to school, witches stayed hidden.
Personally, I got tired of <PERSON> because I felt like all his books are essentially the same and it really irked me that they all began with <PERSON> having a nightmare and being awakened by some authority figure. I thought <PERSON> books were well-written in terms of accessible language but felt it obvious that he "borrowed" his overall plot points from already established works. The one that springs immediately to mind is <PERSON> Dragonrider books. Adults who criticize the writing in Children's lit probably forget the language needs to be geared to kids and most times will have simple sentences and be less sophisticated.
I also notice the books listed in the original question enjoyed a great deal of commercial success. I've known people who are mildly pretentious and think any book that has mass appeal is not good writing because its not literary (I say artsy) enough.
In the end I'd say defining Good writing is like defining Art: "I don't know what it is, but I know it when I see it." Yes, that is subjective and ignores the "technical" execution like good grammar, punctuation, and sentence structure but in the end I think we all tend to label books we like as good writing and books we don't like or fail to "get into" as bad writing. 460