I don't think you'll get much from the discussion there, but the point is, I don't see any evidence yet that there is actually a difference between Wikipedia and Fandom.
On Fandom, admins can delete category pages, but removing the category from article pages has to be done separately. Until seeing a proof that it is different on Wikipedia, I'm pretty sure it is the same.
And what I'm even more certain - it is not related to the version of MediaWiki software.