SteamCMD doesn't strip Steam DRM - even with files backed up (which the Steam GUI will do, no need for SteamCMD), you wont be able to use them without an internet connection and authenticating with Steam every now and then.
GOG's bundles are offline and DRM free. You could store them on a disk, and 30 years from now reinstall and play on an airgapped computer with no authentication required.
GOG's bundles are offline and DRM free. You could store them on a disk, and 30 years from now reinstall and play on an airgapped computer with no authentication required.