Magic is that hard, but being a genius doesn’t make you good at it. Rote memorisation makes you good at it. Hermione isn’t a genius, she enjoys rote learning. Harry and Ron crave stimulation, and there’s none to be found in Rowling’s magic system. Rowling might have intended magic to be easy, but she made a mistake. Rowling enjoys rote memorisation, so it’s easy for her and her self insert, but not for normal people who want to be intellectually stimulated. Rowling accidentally made magic hard, and the story makes more sense with her mistake in it.