I don't think this is true. I say that even though I would be deliriously happy if Rust replaced C++ in most situations it's currently used.
Yes, learning the whole of Rust, including any/all dark corners (no doubt it has a few) is easier than learning the whole of C++ including all its dark corners (it certainly has many!). But getting a basic working knowledge of both is not too different... except for Rust's ownership system. I realise that the ownership system is one of Rust's main benefits, but that doesn't change the reality that it's a significant obstacle for many decent developers.
I actually wish it were possible to use Rust in an "unsafe everywhere" mode where you could ignore the ownership stuff. (Maybe this is already possible with liberal use of the "unsafe" keyword, but it is at least socially unacceptable.) Of course it wouldn't be right for every project but it would still be a huge improvement over C++ while being much more accessible than fully safe Rust.