Furthermore, all the crypto config depends on gpg defaults or your gpg.conf. Whether this is good or bad depends on whether you are OK with gpg's defaults that are chosen for a non-Obnam use case and whether you like tweaking gpg config.
While figuring this out, I started wishing that Obnam used libsodium instead of gpg to avoid configuration and especially gpg-agent. (libsodium didn't exist when Obnam was created.)