you can lay any blame for plot missteps at the feet of grrm
nah.
Agreed, GRRM is not the problem. He provided more than enough excellent source material to lead to any number of satisfying conclusions. It's more like the show runners completely forgot all the masterful work they did on season 1-4, and to a lesser extend 5-6, setting up all these great characters and story lines.
Seasons 7 and 8 are like a completely different show. This isn't a matter of being disappointed with how one character or another ends up - it's a matter of basically putting seasons 1-6 into the shredder. The White Walkers? Turns out not such a serious problem. Jon Snow? Turns out he won't really play any significant role with defeating the White Walkers or Cersei. Jamie Lannister? Turns out after a remarkable arc of character development, instead of completing his redemption he'll return to be buried with Cersei and do nothing of significance. Dany suddenly decides to napalm innocent men, women, and children even though it was completely unnecessary? So, like, she just suddenly goes mad? First Arya takes on far greater significance than she deserves in the White Walker plot line, and then she has absolutely zero significance in the Cersei plot line?! What in the seven hells is this crap?