I'd agree that "what you are able to do" seems like it's intuitively part of expressiveness, but due to Turing completeness you don't have any situation where l

I'd agree that "what you are able to do" seems like it's intuitively part of expressiveness, but due to Turing completeness you don't have any situation where language A can compute something that language B can't. So the only difference in capabilities seems to be in how easy it is to compute something, rather than if one is able to do something.