>> It also enabled a ton of event driven actions which laptops/desktops/embedded devices use.

> Don't forget VMs. Even in server space, they use hotplug/hotunplug as much as traditional desktops.

I was doing hot plugging of hardware awo+ decades ago when I still administered Solaris machines. IBM/mainframes has been doing it since forever.

Even on Linux udevd existed before systemd did.