I don't think so, because there isn't a performance drawback compared to threads when using async. In fact there's literally nothing preventing you from using a thread per task as your future runtime and just blocking on `.await` (and implementing something like that is a common introduction to how async executors run under the hood so it's not particularly convoluted).
Sure there's no reason to do that, because non-blocking syscalls are just better, but you can…
> I don't think so, because there isn't a performance drawback compared to threads when using async.
There is. When you write async functions, they get split into state machines and units of non-blocking work which need to be added and taken from work queues. None of this has to happen if you just spawn an OS thread and tell it "execute this function". No state machine, no work queue. It's literally just another sequential program that can do blocking I/O independently of your main thread.
If you insist on implementing a thread-based solution in exactly he same way that an async solution would, then yes they'll both pay the price of the convoluted runtime. The point is, there's no need to do that.
Sure there's no reason to do that, because non-blocking syscalls are just better, but you can…