It’s slower for two very good reasons (better static analysis and better feedback).

Apparently that's not really the reason. cargo check is usually quite fast.

I also wouldn't say Rust code is slower than C. It wins in some places (e.g. strict aliasing) and loses in others (e.g. bounds checks) but in practice it's usually much faster because it's so much easier to use fast containers (not just linked lists everywhere), fast libraries, and multithreading.