Ok I had to read that twice to understand the angle I think you're coming from, but uh, basically yeah, agree.
If you want a game, that works if the net goes down... yeah, sometimes just 100% relying on vanilla Steam, that'll fuck you.
But, Steam does have ways to set up local backup, freeze potentially breaking updates, work in offline mode...
But but, yeah, in many cases, for many people, it makes sense to just either make and keep your own isolated backup of some kind, or yeah, just grab a rip from somewhere and keep it in emergency storage.