On the other hand, a worse implementation in the stdlib can make it harder for the community to crystalize the best third-party option since the stdlib solution

On the other hand, a worse implementation in the stdlib can make it harder for the community to crystalize the best third-party option since the stdlib solution doesn't have to "compete in the arena". Go has some of these. Maybe a good middle-ground is something like Rust's regex crate where the best third-party solution gets blessed into a first-party package, but it is still versioned separately from the language.