[imtringued]

>Cooperative multitasking tends to break down at scale, because the probability that all the "threads" you're cooperating with are playing nice goes to zero as the number of threads increases.

That's completely wrong. Either cooperative multitasking works or it doesn't. There is no probability involved. What often happens is that foreign code that is not under your control is not yielding. It only takes a single non cooperating task to block an entire core. If you have properly written code the probability of a malfunction is 0% and this probability doesn't grow with the number of threads.