Remember that we're comparing languages, not programs. A language can be thought of as the space of all programs that can be interpreted by that language. In any language, any algorithm can be implemented arbitrarily slowly. So the only meaningful point of comparison between language X and language Y is the upper bound on the performance of each language's program-space.

That some particular C program exists that is at least as slow as a program in some other language is always true, trivially, and so is not a good interpretation of "as fast as C" regardless of its objectivity.