>"C/C++ are in a category of their own."

If one wants to know it all then yes. C++ is huge language. In practice except few people nobody really needs to. Subset of modern C++ enough to solve many real world tasks is very easy to learn in my opinion.

With Rust one must first train brain to wrap around those ownership rules and this might not be easy.

Fortunately or not I do not know even remotely enough of Rust to do the real comparison of "mental load" but at some point I will.