That might be true for the default config in the extension, but you can also configure the extension to de-emphasize fandom wikis or outright hide them in search results. I don't quite remember the exact default config though.
The default config is good for SEO, which is to re-order search results to put independent wikis above Fandom (driving clicks to the independent wiki), as well as disabling Fandom results + injecting a button to the indie wiki.