That is a big may, given that it depends pretty much on what is being done in terms of code, and compile time execution (C++ and Rust), and many of the same compiler knobs are also available for C++ code, if not even more.
And was you point out, at the end of the day it is the same LLVM IR.
That was the point I was trying to make, Zig isn't inherently faster than the other three. It just uses different default compilation options than clang, so any gains can be achieved in clang-compiled C or C++ too by tweaking compile options (and maybe using a handful non-standard language extensions offered by clang). Other then that it's just LLVMs "zero cost abstraction via optimization passes" and this works equally well across all 4 languages.
Or: the "optimization wall" in those languages is the same, only the effort to reach that wall might be slightly different (and this is actually where Zig and its stdlib might be better, it's more straightforward to reach the optimization wall because the Zig design philosophy prefers explicitness over magic)
And was you point out, at the end of the day it is the same LLVM IR.