Nothing, and certainly not Rust, is "perfectly" memory safe.

I agree, which is one of the reasons I think it's a stupid rule to put in place, to begin with. A lot of so called memory safe languages are just built on top of C anyways (which is not considered memory safe).

Granted, it'd be far harder for, say, Ruby to meet those proofs than a language like Rust, but the critical point is to have a defined standard of "good enough" for languages to work towards.

True, but that's what the industry is already aiming for anyways. But vulnerabilities won't stop happening any time soon