We went through great lengths to be able to do parameterized YAML using jinja2 templates. I designed a system that let us effectively create a new yaml out of two other yamls which let us handle repetitive configuration tasks reasonably well but there were occasional unexpected challenges thanks to the syntactically significant white space of yaml.
We were targetting configurations of Concourse for deploying software. We would have to do essentially the same deployment to multiple environments (dev, qa, staging, performance, prod) and Concourse doesn't provide a sufficiently rich configuration in its use of yaml. For a single app cut and paste is acceptable but once you get into multiple microservices, it becomes more efficient to do it this way.
Have you looked into Jsonnet/CUE/Dhall? They attempt to solve this problem, but give you an actual programming language instead. I've been using Jsonnet to successfully escape the 'yaml-templating-yaml' hell for years now.
But yeah, concourse configuration files are probably the worst YAML verbosity offenders, even worse than k8s manifests.
