Its not the fandom's fault when the materials ask for everyone to assume there's a special heritage going on. That's why there was the debate about Rey, it was invited upon and fostered not only in the first film itself but in interviews given by cast and crew afterwards. And when you name a book, even tentatively, Diana's daughter, people are going to assume biological daughter.
I'm not saying there's anything wrong with going in different directions, but at the same time its weak to blame collective fanbases for voicing and debating things they are purposely invited by the makers of the content to assume/ponder.