It does. It also suits very well the use case of the personal computer and other personal devices, as exemplified with macOS and the Steam Deck.

It helps keep the core system free of malware.

I'm not sure about macOS but my understanding is that the Steam Deck does upgrades in a blue-green fashion so if something goes wrong, the previous, known good system is still available.

Immutable base image also reduces chances of software that’s not malware unintentionally screwing things up or putting files in places it has no business putting them (as Adobe loves to do).

macOS obviously has its desktop environment as part of the image, which makes it difficult to accidentally destroy your desktop environment, is that true of SteamOS too? Seems like it’d be smart if the immutable image at least included a minimal fallback like IceWM or something that it spins up if say the package manager loses its marbles while resolving dependencies or something and eats the stock KDE install.