I think there's also some real world components of one queue vs many queues that are missing here. For example, at a hotel checkin, flight baggage checking, or

I think there's also some real world components of one queue vs many queues that are missing here. For example, at a hotel checkin, flight baggage checking, or Fry's electronics, there is one line which feeds into multiple agents. As the number of agents grows, there's a nontrivial amount of time where an agent is done with the current customer, but the next person in line has to walk maybe 50 or so feet to them, wasting some time, especially if they are slow (kids, luggage, elderly).