What is throughput as far as processors are concerned?
Throughput is some measure of the capability of an algorithm to get things done. When you've defined what exactly is your measure, you'll have a better idea of what throughput is measuring. It might mean percentage time servicing all tasks, it might mean time servicing high priority tasks, it might mean something else.
In the case of a Round Robin versus a First Come First Served scheduler, there is obviously a significant latency difference between the two. A Round Robin scheduler is also known as an Alice's Resturant scheduler, as you have to wait for 'the chorus to come around' before your task gets serviced. Under even light load, this can mean that a repeatedly queued task, like a keyboard handler which handles a single character at a time, can take longer than you expect, acting on a queue of key presses one - at - a - time, very tedious.
It's not obvious that either would spend longer swapping tasks so not spending time on useful work, is the task queue pre-emptive, are the tasks active-time-limited? These assumptions, plus some assumptions of the task arrival statistics, and any other relevant constraints like limited memory requiring swapping, would have to be taken account of in modelling throughput.