Martin will kill off an important character because he has no idea how to write a character arc out of a wet paper bag.
I actually don't think that's true. I think what you're reacting to comes with the epic scale of the novel (SoI&F really is just one, long, continuous work) -- both in word count and the enormous cast of characters. It's a kind of literary clutter. If you boiled Game of Thrones down to the story of Ned Stark's rise and downfall, that would be quite a satisfying (although grim) story arc. The fact that the story goes on and on after that dissipates the emotional impact of that one story line.
At over 1.7 million words currently, Song of Ice and Fire is more than six times as long as typical English translations of the Illiad and Odyssey combined. Think about that. In the time it took you to read just the first volume of Song of Ice and Fire, you could have read BOTH the Illiad and the Odyssey. And as a bonus you'd have read BOTH the Illiad and the Odyssey.
As works go further and further north of 200,000 words, they almost inevitably lose the tight, clockwork structure you expect in a 2 hour stage play or 70,000 word novel. Stories stop feeling like they have a beginning, middle, and end and start to feel more episodic. That happens to some stories well before they hit the 200,000 word mark (American Gods, 183 KWords).
At 473 KWords, Lord of the Rings is one of the rare exceptions. From Rivendell onward it's a marvel of complex yet tightly interwoven structure. But it's a hot steaming mess of false starts up until Ford of Bruinen. Tom Bombadil anyone? I think that it could probably be edited down to 400,000 words without losing much artistically. That's still almost miraculously long for a story that feels like one story.
I have a theory about episodic megastories like Song of Ice and Fire, which is that they aren't catharsis you get from a tightly plotted play or novel. They're about transporting a reader to a world he finds interesting to visit again and again. If so that bodes ill for the the Game of Thrones TV series now that Emilia Clarke has sworn off nude scenes.