Overall, I completely agree with you, but I do find that HCL seems to be a pretty good fit for what its used for (at least for Terraform, which I have more experience with than their other tools).
My little story was really just me dumping my thoughts after reading about Stevecode, as someone who made a little language (not a configuration language though) and isn't an argument for doing so at all. I'm definitely in favour of sticking with an existing format for configuration (personally, I like to use TOML or EDN for my own projects' configuration needs, or JSON if its not normally meant to be edited by humans) and even for scripting, normally I'd stick with Lua or Javascript. My language came into existence because neither of those was sandboxed in the way I wanted (it was also deterministic and guaranteed to halt as there were no unbounded loops).