The important point to be made is that the "simpler" tasks will be automated early, pushing human required labour to generally be smarter and better educated.

There are only so many people for any required value of "smart". The historical human computers in the article required less education and base intelligence than the mathematicians that are employed today.*

Sooner or later a significant segment of the population will simply not be able to train to most tasks that still require human labour. And slowly (or quickly) that bar will rise. When I hire and train people I simply need a certain baseline mental capacity, otherwise they will never get good enough to keep, no matter how long they train.

*) Note though that this does not mean they necessarily were less intelligent than the modern work force.