>> C++ still exists because existing projects were written in it... that's it.
That was the claim. Between "Rust exists" and "the only reason C++ still exists is existing projects were written in it" there's still a fair amount of ground for you to cover.
You said that Rust is more memory safe. Hard to argue. And more concise, about which I have no information. Those are good things. But, as I brought up elsewhere in this thread:
Is Rust as easy to use in the embedded space? Is it available on as wide a variety of chips?
Does Rust make it as easy to control memory alignment, for those who need it?
Does Rust make it as easy to interface with libraries, many of which are written in C++?
Memory safety is good. Conciseness is good. Those are not the only reasons one might choose a language.