The real problem is config drift. You have to maintain a lot of little fixes over time as you operate vanilla Linux. I've run fedora atomic (and rebased to bazzite when it got fairly big) since it launched years ago with only one relatively minor hiccup that was resolved by a single line in terminal (rpm-ostree rebase). You can layer stuff over it to modify the base image and clear it if something breaks, whereas manually removing critical packages and being sure to clear every file would be a nightmare on any other distro. It's an extremely hands off experience that works just like git does and is very bullet proof and reproducible.

I like putting it on old people's computers. It's perfect for a seamless experience.

Yeah, a file system snapshot is another way of achieving safe upgrades. There are upsides and downsides of all approaches though.

Rolling back to a btrfs snapshot might be harder than just picking the other ostree image in GRUB. And you still have the problem where old binaries might be running when only the new binaries/libraries exist on disk. But it also saves space on disk compared to an immutable distro, and it’s much easier to make changes to system files. Every approach is a compromise.