Just taking a stab here but I think the idea behind automation is that the automation itself is more cost effective than the human resources, and in turn, yield

Just taking a stab here but I think the idea behind automation is that the automation itself is more cost effective than the human resources, and in turn, yields the same or better results. Thus the human resource pool becomes inefficient when weighing the costs of paying all the humans versus weighing a machine. There's only sense in exploiting a resource if the return is greater than the investment, and since automation replaces a workforce that doesn't require deep specialization, you end up with a resource pool that has little value. The big win for John Henry wasn't that he could keep up with the machine, but he actually exceeded it and was less costly, and demonstrated that a theoretical army of John Henry's were more efficient than an army of the railroad spike driving machines.