I think people who believe Martin had anything to do with this show past season 4 are just fooling themselves. It's pretty obvious by how convoluted the story was and how poorly everything was tied together that it isn't something that Martin planned out or even wrote. We were getting D&D's best guesses as to what their version of what should happen would look like. There's no way you could read the books or watch the first 4 seasons of the show and think that seasons 6 through 8 were anything that was written down or planned out. I don't even believe Martin wanted Bran to wind up on the throne. I think that was HBO's version of the "surprise" ending that most of the other seasons finished with.
Although I put a lot of the blame on Martin and his laziness at finishing the story, I also blame HBO and D&D for rushing the ending so they could fuck off and write the equally bad abortion of a story that was the last Star Wars movie. Even though Bran ending up as king is stupid as fuck, what was even dumber was how rushed the entire ending of the show was. They could've stretched it out to at least 3 more full seasons (not like HBO didn't have the money or the audience), and tied up some of the storylines, and at least given the long night some more magnitude, maybe at least show Dany's descent into madness unfolding a little bit at a time, instead of her going pants on head insane in the course of 10 minutes. Perhaps that would've made it more believable. But how rushed the entire last 2 abbreviated seasons felt, and how nothing made any sense, and how poorly it was written, leads me to believe they didn't have a clue as how to finish the story, and just threw shit at a wall, and that's what we wound up with. As fans of the show, and how amazing the show really was, we deserved better.