I don't think many people rejected the conclusion outright, just the path of getting there. So much of the last season was totally nonsensical. Dothraki ride off into the darkness and get obliterated by zombies; next episode, they're back! Everyone forgets about the Iron Fleet. Jamie ditches a 7 season character arc in a second. Arya subverts expectations and undermines the existential threat in an instant. The all-seeing, all-knowing Bran serves no purpose except to have "the best story" somehow. Dany heel turns from saving the world to destroying it on a whim.

Most of Game of Thrones, books and show, is predicated on causality. Things happen for a reason. And they happen realistically, not necessarily in the way we want. It was a breathe of fresh air in the beginning. Honor isn't rewarded for honor's sake. Strength is a tool, but a slippery slope. Travel takes time. When that realism is thrown out to force plot, it undermines the entire show.

So it's not necessarily the ending that was bad, it was how it got there.

I'm fairly sure the show ending is the ending of the book, but the directors rushed it. Martin is still thinking of a way trying to get from Book 5 to that ending.