… and I think I'd argue that the parent's argument against the tooling would apply equally as well to those "other things", too.

The alternative here is something that manipulates the data structure directly. E.g., it might permit me to say:

  my_config_map.data["key"] = some_string_value

(This is in some pseudo-imperative language, vs. the parent's Lisp, but that distinction isn't particular relevant to the core of their argument, I think.)

And then at the end, the thing itself takes care of converting the resulting objects to YAML, thus preventing me from inadvertently turning what is meant to be a string into something like an accidental YAML-injection that results in terrible errors because I miscounted the number of spaces to indent something.

The funny thing is helm is as good or bad as what you make it. When folks complain about helm they are actually complaining about their own self created charts or poor selection of charts they install.