I was referring to the overhead of development time. Rust is more complex than C, at least, and even after having gained proficiency coding in Rust still takes more time than writing an equivalent C program.

And "zero-cost" is misleading. There are definitely performance impacts from the implicit (and unadvertised explicit) bounds checking some of Rust's features come with. Writing a C program to an equivalent level of safety would have similar performance impacts. Hence, for as close to the same safety as possible, Rust and C should be almost identical in terms of performance.