Same issue here too, I have ICUE (corsair software) which forces the DPI but for some reason the wow opening screen is overriding that. Some hidden mouse setting I think which is by far ANNOYING. I hope it’s not like this once the game launches or I’m going to have words to say.
Edit I think I fixed it.
In config.wtf there are a couple of settings. Set them to 0 should put your mouse dpi back to normal. Worked for me
SET mouseSpeed "0"
SET enableMouseSpeed "0"