Writing unsafe Rust is actually much harder than writing C or C++. C and C++ compilers apply certain optimizations quite conservatively (like anything involving aliasing) because the language doesn't assume a bunch of things like two mutable references never alias. Rust is a lot more aggressive.

If I was asked to rank them in terms of number of things you need to know to write fully correct (no UB) code, I would have: safe Rust < C++ < unsafe Rust

Here's a nice blog post that really resonated with me: https://lucumr.pocoo.org/2022/1/30/unsafe-rust/