Imo, GRRM's original ending was similar to the shows. He even said in an interview years ago that it would end in a similar way for most of the main characters. It's just that D&D rushed the final 2 seasons so much we lost what actually made it good (not enough lead-up, no connecting the dots, inferior dialogue, etc.).
The show needed 10 seasons, at least, for it to make everything work... and it still would've been depressing. D&D just refused to spend more time on it and we got the Cliff Notes version.
GRRM now has the advantage of changing things people didn't like and saying, "That's how it was supposed to end all along".