You seem to be operating under the assumption that the C developers know how to use restrict, when in practice they don't, so it hasn't made the argument fell apart.

In fact, only C++ is able to confortably beat Fortran, despite not having official support for restrict, because of the stronger type system and compile type metaprogramming that offer optimization opportunities out of reach to C compilers.

Usually HPC places like CERN and Fermilab don't migrate their aginging Fortran code to C, rather C++.