> Rust is technically better than C++ in most possible ways — in some, significantly better — and worse in almost no way.

It's much worse in one way: Interoperation with existing C++ code. Sure, that's not a fair criteria - C++ is designed in a way that makes it almost impossible for other languages to use C++ libraries without a heavyweight wrapper like SWIG. However, even though it's not fair, it's still really important. If you have a project like LLVM with millions of lines of existing C++ code, adding expensive or complicated interop boundaries between different components within your system is not an acceptable price to pay.