I'm not so sure. I've a feeling it's easier to write decent Rust than decent C++. The post contains comments about how difficult they found it to keep coding

I'm not so sure. I've a feeling it's easier to write decent Rust than decent C++. The post contains comments about how difficult they found it to keep coding style consistent and language feature use consistent. This suggests to me an inexperienced team without the skills to manage a project of the size and complexity they need. Now whether with the right team they could produce a better solution in C++ or Rust, i've no idea, but if this is the team they have, then it sounds like Rust might be the right choice for them.