I’ve never really thought about it like that, but have to agree with you. Harry is completely devoid of character. As someone who fell in love with reading/fantasy as a result of these books, I loved the wizarding world. I didn’t really have any care for Harry, or even much for the story that he’s a part of - just the setting, and the other characters.
I wonder if Harry’s transparency makes it easy for a young reader to project their own personality onto him, and kind of ‘roleplay’ their way through the series? I think the fact that the wizarding world is ‘bolted onto’ reality facilitates this - it feels almost tangible. May explain why nostalgia is so high among this particular group - it was an experience, not just a story.
Does this make Rowling a genius? Or do her books just benefit from the side-effect of her writing a bad MC?
I would argue that offering fans a template goes miles towards to how… sandboxy the series becomes. (For want of a better term)
For Harry Potter, it was the whole academic experience. How you got admitted, the personality tests; things that enable a safe starting point and allow the fans to go in their own direction.
With Kingdom Hearts back in the day, it was Organization OCs with powers and weapons that followed a template. Similar with Steven Universe and minerals and weapons.