The real difference is in compile-time abstractions. It's much easier to organize things in Rust, especially with a borrow checker. You can confidently remove overhead while being sure that it'll continue to be memory safe.
Yes, Rust's BC is a great technology, but C++ is not a runaway nuclear fire which contaminates and melts everything around it when it comes to sanity and security.
Yes, Rust allows you to run amok by not allowing it, but you can design a good foundation to your code which prevents tons of problems out of the gate in C++, and this is without using smart-pointers and other things available to you.
And there is an almost perfect overlap between the people capable of pulling off a rewrite like this and the people who would write a good C++ foundation in the first place.
I never meant to imply such a thing. However, Rust is simply a much better-defined language. Moves do what you expect, smart pointers work like you'd expect, there are not 3 (or 5) different types of constructors you have to understand and implement properly if you want to build your own abstractions. You don't have to remember where to put std::move, you don't have to remember what happens to the variable after you move out of it, you don't have to use the awful variant accessor functions if you want a tagged union and so on.
Yes, you can do all this in C++. You can build safe abstractions. You can build layers on top of the STL to make it less awful. You can make use of modules and #embed and other nice new features that C++ is getting. But you need to be a lot more careful compared to Rust, because the compiler is not going to help you.
Not sanity, maybe. But security? How much more would it take to declare a nuclear meltdown: https://alexgaynor.net/2020/may/27/science-on-memory-unsafet...