We mean different things when we say "good writer", and you get at it by using "novelist" vs "writer".
When professors or employers complain that their students or employees can't write well, and lament the quality of public education that caused the ineptitude, they are talking about writing as a means of communication. They aren't talking about any of the mentioned parties' inability to produce good novels.
A novel is good if you enjoyed reading it, even better if it has re-read value. A good novelist produces good novels. Whether or not you enjoyed reading the novel actually has nothing to do with whether your understanding of the plot is the same as the author's. In order to confirm that the novelist was effective at using writing to communicate information, that information would have to be known as ground truth on both sides of the channel. As an imperfect example: if you had a chat with the novelist, and it was revealed you had a different understanding of the plot, then they couldn't be that clear of a writer, even if you enjoyed the novel.
When professors or employers complain that their students or employees can't write well, and lament the quality of public education that caused the ineptitude, they are talking about writing as a means of communication. They aren't talking about any of the mentioned parties' inability to produce good novels.
A novel is good if you enjoyed reading it, even better if it has re-read value. A good novelist produces good novels. Whether or not you enjoyed reading the novel actually has nothing to do with whether your understanding of the plot is the same as the author's. In order to confirm that the novelist was effective at using writing to communicate information, that information would have to be known as ground truth on both sides of the channel. As an imperfect example: if you had a chat with the novelist, and it was revealed you had a different understanding of the plot, then they couldn't be that clear of a writer, even if you enjoyed the novel.