If you produce a static binary and can copy it to the server, sure, Docker might be overkill. But how do you reproduce an ensemble of services and their exact version in prod environment? Even just having a stable dev environment by using Docker images with fixed version for database and other auxiliary services is very valuable.
While this is definitely a valid option I'm not sure that introducing Nix/Guix simplifies the stack compared to using Docker. Depends on the setup and experience, I guess.
