There's no way I would say David Benioff is a hack. He did write City of Thieves, which is an excellent novel.
My problem with the show is that it prioritizes twists above everything else. Even breasts. Because of that, scenes are constructed to lull you into peace before the rub is pulled out from under you. It's incredible that the books have exponentially more characters, but more named characters have died in the show. Ironically, the show's reliance and death and twists creates a predictable rhythm where we're trained to expect chaos, which often makes individual scenes rather boring.
The book, of course, does have shocking moments, but they're presented very differently. Instead of trying to spring major changes on readers, Martin instead laces hints and foreshadowing beforehand. This makes it so that every chapter (yes, even in Feast and Dance) are necessary. And, upon re-reads, you can see the groundwork that had been laid out.
I understand part of that is just adapting for the medium. But I feel that it's a lesser story because of that. For instance, killing Joffery hurt the show's narrative because there was no longer a traditional antagonist (other than the purely evil Ramsey). In the books, the lack of a villain isn't a problem. It's a story about morally gray people trying to do what they feel is right for either themselves, the realm, or a combination thereof. Even someone like Euron isn't presented as a villain.
Game of Thrones works for television because it is filled with sex, blood, and twists and eschews the complicated motivations and backstories that fill the books. Although it's a good show, I do find it insulting to its audience. It is possible to have a complicated, nuanced story that takes place in a fantasy universe; HBO just didn't have faith that people would be vigilant enough to watch it.