Samba is using the cifs filesystem - gio is just a layer on top of smbclient functions.
The reason you cannot - anonymously - browse the root of the samba server is because netbios browsing has been disabled due to widespread ransomware propagating through netbios browsing.
Whether you choose to mount the share using the mount command, using an entry in fstab, using mount/automount units or gio, the cifs filesystem is the basic.