Comment by TheAsprngHacker

I said this in my other reply, but if you can implement a language feature as a local rewrite, it does not add expressiveness. Features that add expressiveness must involve some sort of non-local transformation. A language feature adds expressiveness iff two programs that are equivalent in the base language in all evaluation contexts are not equivalent in the extended language. Felleisen came up with this idea in a paper, which Shriram Krishnamurthi explains in this video: https://pwlconf.org/2019/shriram-krishnamurthi/