One very important thing to point out here is that you’re not just writing config with this YML. If you look at the example on the GitHub link it’s a workflow orchestration and execution context. There’s a code runtime involved and logic is executed in the YAML. That is where YAML falls apart.

If all you’re doing is defining configurations (example is Kubernetes manifests helm charts etc) then great. But that isn’t what this is.

To your original question, I would actually advocate using the general purpose programming language for most use cases. Learning a new DSL, like you mentioned, is overhead from both a usability and maintainability perspective. I haven’t used jsonnet before but I know that cuelang gives you some power tools around typing, config validation, templating etc. it’s essentially purpose made for configuration management and tooling so it’s probably going to be really good at that. I don’t know if it’s worth using over a suite of language specific tools like Pydantic + Jinja though because when you’re using a general purpose language like python you have a whole, much larger ecosystem of tools and libraries you also have access to and can pull from.