Drive File Stream is for GSuite users, looks great but we already use Egnyte in enterprise as we need hybrid storage (local in sync with cloud) for performance demand
Google also informs that those still using Drive for Mac or PC will start seeing messages notifying that the service is going away and will urge them to adopt any of the two other tools currently.
The Backup and Sync for personal users is just an expansion of Google Drive. Its much better as you install it and it keeps your Google drive setting and lets you choose other folders from your local disk to sync. So if you have an existing photo library or bunch of stuff you can sysnc that now rather than having to keep it in your Google Drive folder