And as with async, the issue is a) the lack of the ability to write generic code that can abstract over the async-ness or throw signature of a function and b) the ability to type erase asyncness (by wrapping with stackful coroutines) or throw signature (by converting to unchecked exceptions).

Incidentally, for exceptions, Java had (b), but for a long time didn't have (a) (although I think this changed?), leading to (b) being abused.