Many people still have the mistaken belief that C is still trivial to map to assembly instructions and thus has an advantage over C++ and Rust in areas where understanding that is important - but in practice the importance is overstated, and modern C compilers are so capable at optimising at high optimisation levels that many C developers would be surprised at what was produced if they looked much further than small snippets.

Like half the point of high-level systems languages is to be able to express the _effects_ of a program and let a compiler work out how to implement that efficiently (C++ famously calls this the as-if rule, where the compiler can do just about anything to optimise so long as it behaves in terms of observable effects as-if the optimisation hadn't been performed - C works the same). I don't think there's really any areas left from a language perspective where C is more capable than C++ or Rust at that. If the produced code must work in a very specific way then in all cases you'll need to drop into assembly.

The thing Rust really still lacks is maturity from being used in an embedded setting, and by that I mostly mean either toolchains for embedded targets being fiddly to use (or nonexistent) and some useful abstractions not existing for safe rust in those settings (but it's not like those exist in C to begin with).