To be fair, GoT's greatest strengths and moments come straight from Martin's books. When D&D took over, like in season 7, it became more of your generic turn-your-brain-off fantasy epic.
This. The GoT producers are actually pretty bad, and got famous only thanks to the great source material. Everything they did themselves (more and more stuff after season 4) has been sub-par and sometimes even embarrassing (so much plot holes in the last seasons...).
Give them something great already written and ask them to follow it exactly, and they will do something good. If you tell them to create something, you can expect something pretty bad.