Proving the equivalence of particular parts of different languages is really useful: it lets us look at those parts in a different way, & sometimes gives us a new, convenient way to implement useful features.
I would expect programming theorists to be smart enough to recognize that proving equivalence doesn't by itself demonstrate value. Language design is a matter of taking advantage of reframing to make previously difficult-to-imagine tasks easier to reason about. There are no 'cheap tricks' here -- or rather, cheapness is a good thing rather than a bad one. So long as a technique is effective, it's valid.
Now, there's something to be said for criticizing languages for being an internally inconsistent bundling of unrelated ideas. A language that's like this tends to be a combination of copies of different complete language systems. The problem with this kind of language is not that it's unoriginal or trivial but that, because it doesn't have a general philosophy that unifies its components, it is harder to reason about: one must reason about components in whatever chunks have internal consistency, & a grab-bag language has many small universes of consistent behavior that interact in difficult-to-predict and difficult-to-remember ways.