If you need to care about state with systemd you still have the "nonsense" of persistent volume claims, they are just something you keep in notes somewhere, in my experience usually in heads of the sysadmins or an excel sheet or a text file that tries to track which server has what data connected how.

Understand that in the hypothetical system we are discussing, there are something like 1-2 servers. In that case the "volume claim" is just "it's a file on the obvious filesystem" and does not actually need to be spelled out they way you need to spell it out in k8s. The file path you give in environment variables is where the most up-to-date version of the volume claim is. And that file is free to expand to hundreds of GB without bothering you.