The Wheel of Time is a cautionary tale of letting a story/world get out of control. The first three books of the series are as good as fantasy gets, and I mean that. Every bit as good as Tolkien and GRRM. They had plenty of world building but still focused on the overall point of the individual books and series. They also came out every 18 months or so. And the author promised the series would be a total of 6 books.
Books 4-6 were also very, very good, but the scope started to broaden and the books became enormous. Starting with Book 7, set-up, tangents, and new minor characters started to dominant the content of books and the time between publications grew to 2-3 years. Little meaningful happened in Books 7-11, it was set-up after set-up after set-up. The low point was book 10, where honestly, nothing happened, nothing. You could have skipped this book and it wouldn't have mattered.
Robert Jordan passed away after book 11 and the series got so bogged down in minor story lines and characters it became a mess beyond words. Even with giving the new author 3 books to wrap up the series it still seemed like a rush. The conclusion was satisfying to most fans, but it also highlighted that 70-80% of content after Book 6 was unnecessary and pointless.
Stories and characters need to progress to an ending, whatever the ending is. For GRRM, it's Dany's invasion of Westeros and climactic battle with the While Walkers and her dragons. Are some side stories important and needed, of course. But when entire novels contain a majority of this stuff, the overall plot gets stuck in the mud.
I am nervous that GRRM is starting to fall victim of this.