From what I've seen of VyOS using a configuration file that is then used to generate the actual system configuration I'm not really sure its so hard to automate. Take your target state, generate a configuration file in the right format, then send it over and apply.

To be honest this feels more like a limitation in Ansible, which has always felt like a bit of a hacky config management system to me in that the way it functions is generally to run a bunch of commands that gradually mutate the system's state, rather than atomically applying the target state, but then I've been spoiled by NixOS on my personal infrastructure recently.