Rust absolutely lets you control alignment, and use SIMD. I won’t claim to make a comparison to C++ here because I have never done that sort of work in it, but it is absolutely a thing.
There are tons of modern languages that allow low level memory access, including Rust. Nobody chooses C++ due to it being more convenient than modern languages.
What matters most in high-performance computing? The algorithm, sure. What's in second place? Memory alignment.
Memory alignment determines whether or not I can use SIMD. It also determines how many cache misses I have.
Can I fight that battle using Rust? Maybe. Is it as convenient as in C++? Is any other language? as convenient as C++?