I completely disagree.
If I'm presenting situations that would be identical regardless of the player's individual PCs then I'm doing exactly the job I should be doing as GM.
The setting is neutral, as am I when I present it. It's up to the players/PCs to decide how to deal with it, and then do so.
Just because I prefer sunshine over rain doesn't mean the rain's gonna stop when I go for a walk because the world realizes "Oh, that's Lanefan out there, better turn the taps off". The real world is neutral that way. The game world should be also.
Why?
I understand this is your approach to gaming. And as your preference, it's certainly fine. But it is not essential as you describe here.
The game world can be whatever we want. Why must it be neutral?
Completely agree.
However, all of those backstories are intertwined with a very VERY solidly and thoroughly built setting that has a deep rich detailed history that the author could then mine to help create these characters' stories.
Which is the part that's being left out by some here. "Build strong character backgrounds and let the setting take care of itself" doesn't give you Middle Earth, it gives you a bunch of characters operating in a vacuum.
I don't think there's really much chance of crafting a Middle Earth ahead of a game. I mean, it took Tolkien nearly his entire life to slowly craft and revise the setting and then ultimately create a story that used that setting in a satisfying way. He also was crafting a novel, not a game.
What makes a game different from a novel? The fact that the protagonists are not controlled by the author, but instead by individual players. That's a pretty fundamental difference and requires a different approach to crafting the world.
Another fundamental difference is that Tolkien was able to revise his setting and characters as often as he needed prior to publication. He was free to alter the history as needed in order to support the current events of his tale. He was not restricted by what he had previously written....he was able to revise it however it suited the actual story he wanted to tell.
Imagine if that was not the case. Imagine if his audience was privy to every idea or concept as it was first introduced to the fiction. He'd have to change his approach, don't you think? Maybe not commit so strongly knowing that he couldn't revise.
Having said that, I think it's actually okay to proceed with a RPG in this manner. I just know that it's no better than any other approach, and is just as subject to paradox and conflicting details and other flaws. In some ways, even more so.