The theoretical difference in power between a non-Turing complete declarative language and a turing complete one is irrelevant in practice. Datalog is a decidable, declarative subset of Turing-complete Prolog. It's also EXPTIME complete. I don't think we exclude any real use cases by prohibiting super-exponential algorithms.

The problem is shitty config languages. I wouldn't group xaml in the same category as dhall for example.