Before systemd I had Redhat machines with 3 to 4 years of uptime, and now you need to restart Linux after updates....while Windows people rarely and they laugh at you...
If you use the command line to do the update there is no need to reboot, however, the issues that the offline update is trying to solve still stands.
Some programs can crash when all their files are suddenly swapped for new ones. I've seen multiple linux systems bork themselves during an update because the update itself caused the desktop session to crash, which caused the update process to be interrupted just as it was modifying some crucial files, thus rendering the system unbootable.
>> If you use the command line to do the update there is no need to reboot
Completely untrue.
And before systemd, updating sshd or cron usually meant restarting that one daemon. With systemd, core updates can affect PID 1, logind, journald, udev, user managers, socket activation and cgroup state as one dependency graph.
Before, its was replace a library and restart the few daemons using it. Now the same library may be loaded by system services, user services and systemd components, making a clean partial restart harder to verify.
Some programs can crash when all their files are suddenly swapped for new ones. I've seen multiple linux systems bork themselves during an update because the update itself caused the desktop session to crash, which caused the update process to be interrupted just as it was modifying some crucial files, thus rendering the system unbootable.