I have - semi spoiler below (it’s based on what has been shown on the show already but I wouldn’t have put it together if I hadn’t read the books:
That is where the 6th book ends, and it sets up the final arc for the last 3 books. If the show sticks the landing it will both be a fairly satisfying conclusion to the last few seasons and also set the stage for future. Just think of it the way that the first 3 seasons all culminated at the ring gates opening, even though there was a whole lot of side quests.
Another semi spoiler:
I find it oddly satisfying that they seem to be following the books that closely, it says to me that they think they can finish the rest of the story in the future. Maybe movies? Maybe on a different provider? Anyway, they don’t seem to be doing something that is untrue to the universe they’ve created simply because they have been cancelled on Amazon.