Or to be more specific, issue isn't text/templating as such. It is a fine templating language for text.

But to use a text templating language to generate YAML, which is not only structured, making it a bad match for character based templating with no knowledge of syntax, but indentation-based, making the combination almost seem like a joke.

Helm charts must be the worst engineering solution I have seen in popular use. First time I saw it I didn't believe it, that this was something people did, for real.