EDIT:
Well, it depends. If you statically compile everything with C build systems, in that sense, the speed should not differ from generic cargo workload. Although, in most cases, projects written in C are dynamically linked due to several reasons, one of which is code speed. In practice, even huge projects written in C (30k to 10k LOC) build quicker than C++ or Rust.
I'm not pooping on generics, either. Generics is a saviour for correctness and performance. Yet, I want to point out the type creep is still a thing, even though there's little we can do about it.
Anyways, this thread should be better interpreted with humor, instead of technical accuracy.