I think you more or less get the best of all the worlds if you: 1) have a good build-test-release process so updating hard coded values is not so hard or dange

I think you more or less get the best of all the worlds if you: 1) have a good build-test-release process so updating hard coded values is not so hard or dangerous 2) use a language like Haskell that makes custom DSLs easy and automatically well-tooled for the more 'logic-y' configuration 3) possibly use a non-DSL configuration file loaded separately from code for basically 'scalar' things like the VAT rate, etc.