Definitely agreed, once a backup/dump has been taken and those utilities exit, we had better ensure that they are durably on disk. For pg_basebackup and pg_dump, as everything except pg_dump/plain require a target directory for the location of the output result, we really can make things better.
Definitely agreed on fixing it. But I don't think your summary is right.
pg_basebackup in tar mode can be sent to stdout, does not require a directory. And the same for pg_dump in any mode except for directory. So we can't just drive it off the mode, some more detailed checks are required.
