I've done some experiments using Apple's Pkl and CNCF's KCL, which look to solve these problems with a simple "configuration language".
I don't think either have very widespread adoption, though I did hear a while back that Apple is using Pkl internally.
I don't even mind text interpolation in helm that much. Yes, it's horrific, but it really doesn't become problematic until you are having an external system render the text being sent to helm that might be processed again after the fact with Kustomize. Your text might hit literally 3-4 different YAML rendering pipelines before it finally hits your cluster. Insanity
Hashicorp had a similar idea to this configuration language you are mentioning. They named it HCL. We do know how that turned out, but maybe that was more questionable design rather than problems endemic to the approach.
What takes effort for humans, takes effort for AI too.
And yeah, HCL was a horrible design. Anything else would have been better, Cue, jsonnet, dhall, pkl, etc. (I'm not sure which of those existed when HCL was created.)
If your agent is doing this you need to get a much better agent. It should call `helm lint` to find those errors.
For a single source of truth for YAML/JSON such as for Kubernetes manifests, any of the ones you list are fine though and a vast improvement on using Go templates for it.
(Yes I've used all of them - and indeed did the first public talk about Pkl two days after it was open-sourced, after several years of using it internally at Apple).
String interpolation is a pox on the ecosystem, especially given how YAML was only originally a debug helper...