I have heard it said that GRRM wrote his books more like a screenplay or at least as if he planned to adapt it to such. The creators of the Expanse did something similar which makes sense since they worked under GRRM before publishing the series. But even with that taken into account a BUNCH of stuff in the Expanse was changed for TV.
Wot and The Expanse are my top 2 book series and the their respective shows are in my top 5.
Whether or not RJ wrote it like a screenplay or not does not change the fact Rafe sidelined Rand, totally changed the magic system, destroyed the Dragon plotline, and maligning characters for no reason.
Change the names of the character and places and the TV series would never be mistook by book readers as the same story.
You have a very low opinion on people that will commit to a 14+ book series.
In my experience people that read fantasy tend to take the lore pretty seriously.
I liked the ta'veren concept, it fits the the theme of the books, time is a wheel and the wheel weaves as the wheel wills, but ta'veren are threads with a purpose that the wheel must weave around.
As showrunner the buck stops with him, he get the glory if it is a hit, he also gets the blame when it fails. See Dan and Dave from GoT, they went from heroes to zeros.
Showrunners generally quit if they feel the show is being taken down the wrong path by Execs, they also have the power to fire bad writers, so yes he gets the blame.