Confusing the main argument with McGuffin is a narrative technique in Eastern Europe? That's absurd. And I´m not talking about real life. I´m talking about a narrative. And narrative has to observe rules. And one rule is "you don´t write thousand of pages about a prophecy, the destiny of the main character, races of elves, a great genealogical experiment, etc. if, at the end, nothing of that matters for the conclusion of the story". If the story is about Geralt, Yennefer, Triss and Ciri, I´m OK with that. Actually, is the part of the story I like. But then, why to write four or five books about things that are not important? I'll tell you: because if the author only writes three books and remove all the filling in the story, he would miss the money by the other five.
About the ending, I would expected that the main characters don't die during a random riot killed by a random character. And, if they are dead, are deat, the thing of Ciri and Avalon is just stupid. They are not "rex quondam, rexque futurus".
Seems like you did not actually get what I wrote. Notice, how I did not actually argue whether it is a McGufffin or not.
Writing a good story is not something that has an exact ruleset. There is no single way to make a good story.
There are certain proven guidelines that, if followed, would generally make for a good story. That is it. That is all there is to it. Those are not mathematical formulas, where deviation may mean that you failed... those are guidelines.
Notice how many of the classics of the given genres are NOT completely formulaic. Many for example depend on their characters to make the "scenes" and the characters. Others dont ACTUALLY depend on characters as much, rather concepts or even the environment. Some of them fill the entire world with a metric f*ck ton of detail (Tolkien... ) or try to keep it as short and to the point as humanly possible. Both are VERY valid approaches. Sapkowski is one that tries to keep some balance really.
Basically... literature is not as formulaic as you seem to think it is
And it NEVER has been.
As for the actual examples you are using, pretty much everything Sapko wrote has its reason to be there. Some of it is *FLUFF * (this is NOT bad, contrary to what some people may think), some of it is used to NAIL down world states and suggest possible future but outside the scope of the story, events. Some, still, is used to build up characters and the themes associated to those characters. Eredin and the Wild Hunt for example.
BTW, removing "filling" is also not a rule set in stone. If you want to remove filling, ALL of it, you will end up with ... what was it, 6 basic tales that humanity is CONSTANTLY reusing over and over again, except with different dressing.
In real life, people often die due to seemingly random things. A random villager too is a his own story, his own idea and his own hero in his own little world. It is random for a "central" figure to die from one that is not... maybe... but THIS is something that happens in real life very often. And this now is part of what I was talking about (as something Eastern Europe seems to like to dabble in... at times). The mortality, randomness... like a twisted fairy tale parody