Having developed a fair amount of expertise with both C++ and Rust, C++ is on a completely different level of complexity from Rust.
In Rust, for most users, the main source of complexity is struggling with the borrow checker, especially because you're likely to go through a phase where you're yelling at the borrow checker for complaining that your code violates lifetime rules when it clearly doesn't (only to work it out yourself and realize that, in fact, the compiler was right and you were wrong) [1]. Beyond this, the main issues I run into are Rust's auto-Deref seeming to kick in somewhat at random making me unsure of where I need to be explicit (but at least the error messages basically always tell you what the right answer is when you get it wrong) and to a much lesser degree issues around getting dyn traits working correctly.
By contrast C++ has just so much weird stuff. There's three or four subtly different kinds of initialization going on, and three or four subtly different kinds of type inference going on. You get things like `friend X;` and `friend class X;` having different meanings. Move semantics via rvalue references are clearly bolted on after the fact, and it's somewhat hard to reason about the right things to do. It has things like most-vexing parse. Understanding C++ better doesn't give you more confidence that things are correct; it gives you more trepidation as you know better how things can go awry.
[1] And the commonality of people going through this phase makes me skeptical of people who argue that you don't need the compiler bonking you on the head because the rules are easy to follow.
The C++ 11 move semantic is definitely an example of C++ programmers being sold a "pig in a poke"† The claim in the proposal document was that although this isn't the "destructive move" which programmers wanted (and which Rust had by 2015), the C++ 11 move feature can be realised with less disruption and is just as good. In reality it left significant performance on the table and you can't get it back without significant further language change.
† This phrase would have been idiomatic many years ago but it is still used with the same intent today even though its meaning is no longer obvious, the idea is that a farmer at market told you this sack you can't see inside ("poke") has a piglet in it, so you purchase the item for a good price, but it turns out there was only a kitten in the bag, which (compared to the piglet) is worthless.
Copy by default is the right way to go. Even if less performant, it’s safe and super-easy to understand. Let the people that want to squeeze the last drop of performance worry about moves…
Move by default is the thing which complicates Rust so much.
In Rust, for most users, the main source of complexity is struggling with the borrow checker, especially because you're likely to go through a phase where you're yelling at the borrow checker for complaining that your code violates lifetime rules when it clearly doesn't (only to work it out yourself and realize that, in fact, the compiler was right and you were wrong) [1]. Beyond this, the main issues I run into are Rust's auto-Deref seeming to kick in somewhat at random making me unsure of where I need to be explicit (but at least the error messages basically always tell you what the right answer is when you get it wrong) and to a much lesser degree issues around getting dyn traits working correctly.
By contrast C++ has just so much weird stuff. There's three or four subtly different kinds of initialization going on, and three or four subtly different kinds of type inference going on. You get things like `friend X;` and `friend class X;` having different meanings. Move semantics via rvalue references are clearly bolted on after the fact, and it's somewhat hard to reason about the right things to do. It has things like most-vexing parse. Understanding C++ better doesn't give you more confidence that things are correct; it gives you more trepidation as you know better how things can go awry.
[1] And the commonality of people going through this phase makes me skeptical of people who argue that you don't need the compiler bonking you on the head because the rules are easy to follow.