YAML is meant to be written by humans. If some lunatic insists on some expression evaluation system, then it should be ${expression} where the YAML file is parsed as is without a template, and the software that reads the YAML file interprets the expression.
If you hate YAML instead of Helm for their insane choices, then enjoy barking at the wrong tree for the rest of your life.
I've been using application.yml files for 9 years without experiencing a single YAML related issue and I see no reason to switch to any other format.