From my short time with proxmox, I had to dive into the command line to do configuration at the host level that couldnt be done with the UI. I think nixos will help replacd those ad hoc configurations with nix options. In the many articles I read about gpu passthru, and also doing harddrive passthru, I had to work in the host debian environment.
I dumped proxmox because I couldnt get gpu passthrough to work, and havent looked back. Nixos modules and docker have served me better than VMs for my usecase.