Fstab is still there untouched, it’s the temporary units files that get replaced at reload.
The mount program works as normally, if you edit fstab and then mount -a
it will work as expected, it will just warn you that systemd is not aware of the change. It will reload it anyway at the next boot.
daemon-reload is not daemon-restart, it just makes systemd re-read the configuration to make it aware of the changes, but the services don’t get restarted. Some services (e.g. nginx) can re-read their confuration without restarting, those services are also made aware of the changes when reloading and can be reloaded individually.
You can edit any systemd units using systemctl edit
so you don’t need to reload (fstab is not a systemd unit)
It doesn’t replace the editor, it creates a stream and opens it in your default text editor. When you write out, it saves the stream to an appropriate drop in file