Mustrum_Ridcully
Legend
What mess? And who is in it?
rounser is. The rest of the world, not so much.

The strong tie between crunch and fluff is not what makes D&D IP worth so much. The fluff on its own is what makes it powerful. Because it is inspiring for creating new stories.If this were the case, the D&D IP would be worth little
Illithids as tentacled humanoids that read minds and eat brains are an interesting theme. But you could implement this theme in any game system.
But I agree with you that fluff is not irrelevant. It inspires us to create stories around it. It's why every D&D edition and many OGL "variant player handbooks" had at least an implied setting. It gives a starting point, a common frame of reference.