I just successfully used Skicka to download my Google data, including gdoc files which (which are links if you don't get the data and do a manual conversion). Great tool. Had to start from scratch, installing Go, and then working through the Oauth process. It feels like Google doesn't want to make interoperability too easy. Only issue (and it's minor) is that the gdoc files download without an extension, which confuses the PC world. Easy enough to clean up afterwards using the Unix/Linux 'find' command.
Thanks to the development team!