I'd be curious to see any examples you might have to back-up any of your bulleted claims since I don't much agree. I think sister / B-side albums are a great way for artists to extend their era and stay creatively involved with their material in a streaming era. Whether it's a set of reject tracks (ala Emotion/Dedicated side B), a quick follow-up (folklore/evermore), or a follow-up deluxe album (positions, Future Nostalgia), all are smart ways to keep eyes on the artist.
Sweetener, TUN and Positions are absolutely not sister albums lol, they both sound entirely different and are thematically varied. Sure, Ari's always going to be a pop/r&b artist at her core, but with each album she infuses something different (EDM, trap, so on).