I would be fine with this statement, if the books didn't give us storybeats that bleed into the leveling experience/main story beats of the expansions. Leading NPC's nowadays talk about stuff that is strictly from the novels and that takes players out of the experience. It's not the case of simply adding to the world, even plenty people that dedicate their time to the endgame tend to enjoy the story as well and this practice is doing them a disfavor. This wouldn't be a problem if you had options during quests to simply ask "what are you talking about?" and get a little summaration of the books content. This isn't the case though and that's why this rubbed me the wrong way since they started doing this with the expansion accompying novel, which wasn't always a thing. Older novels are more like what you're describing and with those I'd agree with you on this, not with the newer ones. The Sylvanas one apparently was meant to give insight to her motivations, which might've helped untangling the current storymess. That or the book is indeed meant as additional context for whatever 9.2 is meant to be.