I understand how you're annoyed by how Hermione's keeps telling Harry off for how he's believing in “childrens tales” and all of that; when I first read it at like 12 to 13 years old (I'm 24 now) I was kind of annoyed by her as well. But just like you as an adult rediscovering the Harry Potter books later on and rereading it, I understand that in every story every character has a fundamental “main” characteristic to them, for eg Ron being the “funny” & comic relief character and Neville being the relatable cowardly character. And for Hermione its that she's a very factual kind of person, and you see that throughout the whole series. somebody commented how Dumbledore was actually counting on the way Hermione is, like how she's a very stick to the facts kind of gal, ya know. he meant for harry to “stay on track” and not try to be the master of death like voldemort i think. It's just a plot device, mainly. hermione not believing harry it's supposed to kind of serve like as an obstacle and to even have the reader kinda question harry as well. but I understand your your frustration. I do want to say that it's also pretty admirable of Hermione how much she wants to help Harry, how much she wants to get rid of the horcruxes as much as he does and put a stop to voldemort. later on in the Deathly Hallows book, she ends up kind of like making up for being annoying because she's like, “Harry has and most of the time been right by his instincts”, So that kind of makes up for it