Well that is a good analysis! You honestly got me more convinced of Harry's personhood than the books ever did. I guess I just really, really hate Harry as a protagonist, which blinds me to the other points. I'll blame Rowlings writing style for that one though.
And yes, I fully agree about the later books; after the fifth one, I can barely remember anything that happens in them, outside some biggest plot points. Compared to how I can still fairly well recall what happens in books 1-4, and mostly 5 as well despite there being more time passed after reading them, the contrast is huge.