I wouldn’t worry too much about technical comparisons at this point. What’s going to differentiate adoption of languages like Jsonnet/Dhall/Cue are the “complete experience” they provide (e.g. integrations, ease of installation, documentation, available packages, support/knowledge-base, well-developed use-cases, etc.)
However, even addressing the technical aspects the main issue I see with Cue is that it doesn’t really improve much on Jsonnet + JSON schema. There are only a few minor things that its validation system can do that JSON schema cannot do. For example, JSON schema can handle regex-based validation, minimum/maximum values, and untagged unions, too.