This was a seven book mystery. Rowling had several important story lines that she was keeping hidden. Thus she kept many things mysterious and misdirected us on others. It was very easy for readers for be hoodwinked by these deliberate and important deceptions. Also people bring their own emotional and personal backgrounds that influence how they interpret what they read. I would have thought that a linguist would know that comprehension is influenced by personal perception and cognition. That's why I said the dissonance was cognitive dissonance: the inability to reconcile a personal belief with conflicting data.

We still have people who think that Harry and Hermione were destined for each other, yet Rowling didn't write that. She wrote a warm friendship with Hermione as a surrogate sister and the fans misread it.

Snape wasn't meant to be a great figure in literature, but he was a complex and interesting character. Harry wasn't meant to have a big emotional reconciliation with Snape, because Snape was the one at fault. At least Harry did honor his memory.

It's unimportant that Rowling didn't foreshadow all the events in Hallows, like the cloak. Stories can grow and change.

I still see people blaming Rowling for making Snape an unpleasant person or not vindicating his behavior in the end. Why? He would have been a boring character.