> It seems weird to add all this syntax and not have any way to leverage it during runtime.
Just because they're not leveraging them today, it doesn't mean that they won't do it tomorrow. If a proposal requires a big effort to implement it, it will probably never become adopted.
I think it means exactly that. If JS will get type hints that are not checked at runtime then we will never get runtime validation for these type hints since it will break a lot of existing code that has would have "wrong" type hints.
Just because they're not leveraging them today, it doesn't mean that they won't do it tomorrow. If a proposal requires a big effort to implement it, it will probably never become adopted.