Yep I subbed to HBO to get GoT a couple of hours before "other sources" and immediately cancelled mid-way through last season. Night-time fights were just pitch black and a few smudges moving around the screen.

They probably just throw the thing into ffmpeg with the fewest amount of arguments that satisfies a codec and bandwidth cost metric and call it a day.

However, I've never had any problems under the same situations on Netflix using a "blessed" 4K HDR10 set-up (Fire TV Cube and a cheap Hisense TV).