In fact as a configuration file, spreadsheets are a much superior UI, you can change lots of numbers very quickly if your config is tabular in nature. Whether it is a good idea that what you type should modify a prod environment live is a different question. Working in finance and living in spreadsheet it sounds like a terrible design to me. You want to be to inspect the whole config change before it affects the target system.
Also in spreadsheet you can do proper computation, reference other values, make VLOOKUPs. So much better than YAML where the entire ecosystem seems to pretend there isn't a need for abstraction in configs.
