I don't understand the animosity towards the game. Rowling had nothing to do with it. She actually wrote those shitty Fantastic Beasts movies and nobody gave two fucks if you went and watched those.
I think it sucks because from what I've seen, it looks like a fun game. A single player, story based game with no always online DRM, battle passes, or microtransactions, and its based off a popular IP that approaches it with understanding and respect for the IP. At least from the screenshots Im not seeing spike green haired badass millennials spouting annoying self aware quips.
Does it suck Rowling is a piece of shit? Yeah, it does. Do some of her stories suck? Yeah, they do.
But like you said, she has nothing to do with this game.
I might play it someday. I can tolerate Harry Potter well enough and it does look visually interesting if noting else.