Rowling was writing about grade school kids going to school. Grade school kids get bored at school. If they live in a world where everyone uses magic and it’s not that special they’re going to get bored of learning about magic sometimes. It’s like if in grade school our teachers spent a bunch of time teaching us how to use computers, phones, and other technological devices. Sometimes it would be cool and interesting and a lot of the time it would be pretty damn boring.

Plus Rowling wanted the grade school kids reading her books to relate to her characters, so she gave her characters a schooling experience they could relate to. And as much as I hate Rowling, there’s something inherently kind of comedic about a bunch of kids being bored silly learning about magic because it’s something that seems like it should be exciting to us, the reader.

The boredom of the characters isn’t a failure of the writing or magic system, it works perfectly well for its intended effect.