Works just fine for who, though? Not for non-technical people.
The FOSS community, especially the Fediverse community continually disappoint me by being so dismissive of, or even hostile to design critique. Nearly universally, trying to engage a project community in rethinking an interface is received like unsolicited criticism of someone's physique. Even as a software developer who's put many thousands of hours into FOSS development, AND a professional designer, And making it clear I'd be willing to research, design, test, and implement myself, the results are usually just as discouraging. I've stopped trying.
Without significant designer input, FOSS social media initiatives will always be two steps ahead technically but 10 steps behind in UX. After the November bump, Mastodon had lost the majority of the active users it had gained by February. I think that if something even comes close to a commercial social media UX, they stand a chance at being a real turning point the world's conception of how social media 'works.'
Your post cites no specific reasons why Kbin is worse than Reddit from a UX perspective. Have you even tried it?