I have not personally used C++ or Rust in this context, so I can’t speak to the ease of either, so could you say more?
The use-cases I know of basically build a library exposing the C ABI, which is slightly annoying but effective. I'm guessing you're referring to Swift <-> C++ interop?
What I mean is that adding C++ files to your iOS project and having them compile and work together without any new compilation steps or settings, and to have Swift code call a C api on your C++ implementation -- all of this is straightforward to do for iOS, and Xcode even creates the "bridging" headers for you and has built-in support for C++. Now, adding Rust into the mix? That will be much more involved and certainly not as simple; nor is it natively supported by the iOS toolset in Xcode. That's what I meant when pushing back on your notion that "Rust is just as capable at integrating with the specific platforms you're talking about."
I wasn't trying to claim that they're equivalently easy: just that they both have the same capabilities, there's nothing special that one can do that the other cannot.
Maybe it’s possible but definitely not as straightforward to use rust on iOS. Compared to C++.