Among those who have tried both, I can confidently say that the idea that C/C++ parallelism is as easy to achieve as parallelism in Rust is very much a minority view. There's a reason why nobody tried to parallelize CSS styling in a production browser before Stylo came along.
I've parallelized emulators in C++ and work on parallel parts of Bevy now, which is probably the closest you're going to get to someone who has worked on parallelizing parts of large game engines in both C++ and Rust. It was far easier in Rust.
