For hosts auto updates looks like switch that says “enable to make more money and ruin someone else’s day” and like… but what’s the downside!?

As a user why should I tolerate my things being broken by someone for the sake of improving nebulous average case out there?

And that’s already happening, my last WP host’s automated updates system broke updates for me, because my case wasn’t perfectly average.

Auto updates aren’t about average, they are about the worst thing that they can and will do to someone. In WordPress people are being awful casual about that and hiding behind average isn’t advocating for users’ benefit here.