I would argue that rewrite in C++ will make it a lot better. Rust does have some nice memory safe features that are nice enough that you should question why someone did a rewrite and stuck with C++, but that C++ rewrite would fix a lot.
That said, I still think it's a rather weak argument, even if we do accept that the rewrite will do most of the bug removal, since we aren't stupid and move to smart pointers, more stl usage and for each loops. "Most" is not "all".
By contrast, my experience with C++ to Rust rewrites is that the inability of Rust to express some useful and common C++ constructs causes the software architecture to diverge to the point where you might as well just be rewriting it from scratch because it is too difficult to track the C++ code.