unsafe rust is less safe than C++ because of the provenance and aliasing semantics that unsafe rust must adhere to to avoid UB, which are generally tricker than those of C++
The provenance rules in the C++ standard are basically just a shrug emoji†, so it's unclear whether those are worse, I can see an argument for the idea that obeying Aria's strict provenance experiment rules in Rust is easier - not because it's easy (although for many common cases it is) but because at least these are coherent rules.
† U+1F937 person shrugging