The plow (and other technological advances) did make the farmer (relatively) obsolete. The great majority of farmers have gone out of business in the last hundred years or so. That's why there are so few farmers now.
The former farmers found jobs because plows can't work at factories, call centers, KFC, etc. Sufficiently smart robots could. That's why analogies with previous technological advances don't work.
A more relevant comparison would be with horses and machines that replaced them pulling plows, hauling stuff, etc. Where are all the horses, mules and oxen now? Were they freed from unnecessary drudgery to specialize in labor where they had a competitive advantage, or did they suffer severe declines in number, surviving essentially as pets and museum pieces?
Once there is no work that humans do better than robots, there will be no work for humans to do. This could be very good, or very bad. We're not yet to that point, however.
The former farmers found jobs because plows can't work at factories, call centers, KFC, etc. Sufficiently smart robots could. That's why analogies with previous technological advances don't work.
A more relevant comparison would be with horses and machines that replaced them pulling plows, hauling stuff, etc. Where are all the horses, mules and oxen now? Were they freed from unnecessary drudgery to specialize in labor where they had a competitive advantage, or did they suffer severe declines in number, surviving essentially as pets and museum pieces?