You seem to be presupposing that all, or much of the C/C++ written today will follow best practices and be written by "expert" programers. A portion will, perhaps even a substantial portion, but I'd be willing to wager a far larger portion of the Rust written today will follow best practices and doesn't have to be written by expert programers. This is because the safety in Rust isn't optional, like it is with C/C++ best practices/new features.