I think the confusion comes from the meaning of stable. In software there are two relevant meanings:
Unchanging, or changing the least possible amount.
Not crashing / requiring intervention to keep running.
Debian, for example, focuses on #1, with the assumption that #2 will follow. And it generally does, until you have to update and the changes are truly massive and the upgrade is brittle, or you have to run software with newer requirements and your hacks to get it working are brittle.
Arch, for example, instead focuses on the second definition, by attempting to ensure that every change, while frequent, is small, with a handful of notable exceptions.
Honestly, both strategies work well. I've had debian systems running for 15 years and Arch systems running for 12+ years (and that limitation is really only due to the system I run Arch on, rather than their update strategy.
It really depends on the user's needs and maintenance frequency.