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No, you’re still not understanding, say libX current version is 1.2.3 and we have two distros A (a stable distro) and B (an unstable distro). libX now releases 2.0.0, A remains on 1.2.3 B moves to 2.0.0. libX now releases 1.2.4 which despite being just a patch breaks everything. A update and breaks, B does not.
Stable just means stable API, it says nothing about system breakage. System breakage can happen regardless of stable API, and it’s up to distro managers to not release a package that breaks their diatro, and the Arch ones are excellent at their job. An update breaking Arch is as likely to happen as on Ubuntu, but an upgrade on Arch can break other stuff which on Ubuntu can only happen when doing a version upgrade.
If you want to talk about breakage we can, as long as you understand that’s not what people mean when they say stable. About breakages Arch doesn’t break that often, or at all, I can’t recall a single time my system broke for an update or for something that was not entirely my fault.