Agreed. I just wrote a different comment about how the show was clearly declining once GRRM left, even though they had plenty of book material left. So I think the bigger factor was GRRM holding their hand, rather than the presence of book material to adapt.

But you are also correct. The show had plenty of changes from the books which were at best mediocre. And it's quite clear that the show exceled due to basically everyone bringing their A-game, even if D&D themselves weren't great.

The acting was incredible early on, yet became atrocious by the end, even from actors who had proven they know what they are doing. Watching any line from Jaime or Tyrion in Season 8 makes me want to die, knowing how great those actors used to be, and how much they phoned it in.

The wardrobe was also much better early on. By the end, it just became overly generic and trending toward modern. It lost the sense of place.

I know I spent more time ragging on how those elements declined by the end. But the point is mainly that those things were incredible early on. So the show would still likely be carried by talented people surrounding D&D, even if they themselves have no talent.