I think that's essentially what such a service would do. You might throw in some periodic less frequent syncs (maybe you sync down to the main backup every day

I think that's essentially what such a service would do. You might throw in some periodic less frequent syncs (maybe you sync down to the main backup every day and sync that backup to a secondary backup weekly or monthly) and maybe some of those successive syncs are done to hosts that are usually disconnected from the network to add in a firebreak.