> years of bug fixes and edge-case improvements can't be accounted for by simply using a newer/better code-base.

Partially is in fact true: Just because the Rust use a better type system (after ML) + better resource model (aka borrow checker), and if you are decently good, you eliminate, forever!, tons of problems.

It can't solve things that arise by complex interactions or just lack of port subtle details like in parsing poor inputs (like html) but is true that changing the language in fact solve tons of things.