The distinction between Wizard's Hall and Harry Potter addressed in Ugly Prequels is important to point out to the Potter-adults who were once Potter-children. When we evaluate the fandom and politics of the JK Rowling persona and its adherents, we need to do so remembering how they are themselves their own nadir. The comparative failure of Wizard's Hall alongside the comparative success of Harry Potter shows us that, if Hermione had been written as black, all of the Potter-people would not have liked it.
The failure of Wizard's Hall to achieve the vast sociopolitical goals that Harry Potter was later able to achieve, despite sharing the same features, proves the racism of the Potter-children. Even given the same pun-riddle boarding-school fodder dressed up with British accents and magically moving pictures on the school walls, they spat back up the first book since it included a black girl instead of a white girl. They had their chance to have the Potter phenomenon a few years earlier, and rejected it for being too ethnic. Once Hermione had been gentrified, they were waiting in line at midnight. Suburban hypocrisy at its finest: the great proponents of imaginative universalism want their kids to go to a 99+% white/NE-Asian school. And that's all they want to read about, too. But once their beloved childhood story is over, they're safe in the high-rent district while raging against Brexit.