https://wiki.musicbrainz.org/Style/Artist/Featured_artists is basically a combination of guideline and how-to (with emphasis on the how-to part). That made some sense, originally, since artist credits were a new, fairly undocumented thing. Now we have https://musicbrainz.org/doc/How_to_Use_Artist_Credits for the how-to, so the guideline should be simplified to have only the actual guideline bits - any needed extra guidance can be added to the how-to page.