This article makes some assumptions that could easily change the result. By the way, if you have a batch size of 1 you're back to the initial hypothesis which is obviously not how things work in the fast food industry. I think it misses the point of idle time and availability. From the supply chain theory, if your resources are always 100% busy, your delivery time will go infinite because as soon as something takes a little more time as expected then you can never catch up. This applies particularly well to software engineering.