Any source language can be said to be a simple transformation of its target languageNot always. There are a number of language features that have non-local implications, such as pattern matching, lazy evaluation, continuations, or exceptions. If you implement such a feature on top of a language that doesn’t have it, you will have decidedly complex transformations.
I agree that it’s overly simplistic to suggest that it isn’t a full language if it only involves local/simple transformations, but the question of local vs. non-local transformations at least hints at the idea that a new paradigm or way of thinking about programming is involved.