I disagree. For sure there doesn't exist anyone out there who knows every detail of Rust (or any similarly complex project) because that's simply not possible, but domain expertise is a very real thing and simply invaluable to the long term success of any project.

From my own work experience, the "dinosaurs" are the most valuable people in the whole org, because oftentimes understanding the code isn't nearly sufficient to make good long term choices. You very often need to know the historical context of why certain things were made in order to not shoot blindly in the dark with random changes.