I'm not saying art should exist purely for the sake of entertainment. But, ultimately, if I'm investing the time to read a book, I need to get something out of the experience from moment to moment, and generally I find I get more from reading a bad writer with fun ideas than an expert stylist who makes no concessions to enjoyment.
"Some books you read for the story. Don't be like the snobs who won't read a book for the story. Some books you read for the words. Don't be the kind of person who won't read a book for the words either. But when you find a book that you read for the words and the story... treasure that book".
I certainly agree with your assessment that one wouldn't read a King book for the words, but as someone who really likes the scifi-fantasy genre, that's not a standard to which I can afford to hold the authors I read...