`std::variant` is a clever piece of template hackery, but it doesn't come close to Rust enums. `std::variant` has no named variants, no pattern matching, no exhaustiveness checking. In Rust, it's not unusual to have an enum with dozens of variants, good luck doing that with std::variant.

I'm sure you could technically emulate all this in C++ is you keep throwing template metaprogramming at it, but at that point anything is a C++ subset and the statement loses all pratical meaning.