I think I generally agree with this video. I have been spoiled many times. Star Wars, Game of Thrones, etc. I still enjoyed these stories immensely.
I think that spoilers only affect negatively when the story relies on cheap twists that doesn't make much of a sense and are there just for shocks. Prime example I have is Frozen. I was spoiled that Hans was a villain from the start. So I was looking for the clues and hints throughout the movie... I didn't find any. That twist really is out of nowhere.