C++ has accumulated complexity over decades, and the committee is working on making things easier for beginners. Usually it works, mine-fields like string_view aside.
Rust has accumulated its complexity over four years, and it's already comparable to C++. The thing that worries me the most about Rust, is how the language will look like in another 10 years.
C++ is so complex no-one can really grasp how complex the language actually is.
C++ is not slowing down. C++ is on the verge of deprecating STL-style iterators in favour of Ranges, and modules and concepts are imminent. Template metaprogramming is being superceded by constexpr. Of course STL iterators, header files, and template metaprogramming are still going to be around, people will just need to learn all of it if they want to work on a variety of C++ projects.
Rust has accumulated its complexity over four years, and it's already comparable to C++. The thing that worries me the most about Rust, is how the language will look like in another 10 years.