>I only see his nursery as being useful when you really want your async tasks to complete before the function in which they were dispatched returns. That's far from covering every use case of concurrency!

Perhaps, but only having a complex solution that handles 100% of use cases is less desirable than having a simple one that handles 80% of the most common use cases PLUS the ability to go deeper and use the complex method (if, and only if, it's necessary...)