As a bonus, the resulting Docker image is bit-reproducible and recipients of the image can "map it back" to the original Guix revision.
https://guix.gnu.org/manual/en/html_node/Invoking-guix-pack....
That's cool. And I can imagine cases where it's useful.
Stuff like Nixery isn't itself enough to claim "nix is better than Docker", though. -- The questions I'd want to think about are "what happens when I run into a problem? how hard is it to fix this?". I feel like Nix does solve some problems that I've had with Dockerfiles. But there are also problems I've run into with Nix that I wouldn't've had with Nix.
I like nix well enough. But I've also used it enough that I'm not surprised if people have difficulties with it, and are more comfortable with other solutions.