That may be technically true, but in practice some language features require more overhead than others. If a language requires a feature where making it "fast"

That may be technically true, but in practice some language features require more overhead than others. If a language requires a feature where making it "fast" is so difficult that nobody can implement a fast version of it, then I think it's fair to say that language is slower than the alternatives. Knowing that language X can, in theory, be faster than language Y does me no good at all if there are no implementations of language X that are actually faster than Y.