Yeah, yeah, there will still be niches where people will be needed, but that's just it, niches. In the past one large manufacturing plant could employ thousands, or even tens of thousands of workers.
And people looking back at history seem to gloss over the number of niches that have always existed. How many niches existed at the height of steam power to keep a locomotive on the tracks and running?
With respect to the trades there wasn't just one type of woodworker unless you lived in a small town. A person that specialized in cabinet building would have a completely different set of tools and skillsets than someone that built homes. One person could probably do both but would do neither as well as the people well trained to do one.
100 years ago a small town doctor was the Ob, Surgeon, General practitioner and mortician. I'm amazed at the number of sub specialties my wife works with. You have people that specialize in pediatric nephrology. They spend their entire career ONLY working with kids kidneys. Other than med school they have none of the same training as a orthopedic sports surgeon. And for each of those doctors there are dozens more specialized supporting staff. Directly you have nurses and the such.
Indirectly you have the people that built the tools used in the specific industries. The medical hardware and tools that a surgeon uses are different than those that a nephrologist uses. There are hundreds if not thousands of engineers building, testing and working on each of the respective tools.
As the world becomes more diverse the number niche of jobs increases dramatically. It's not like you go to college, become one of 5 professions and do that. I'm one of 50 engineers at a single facility making a single product for a single industry and only 10% or so of my job may overlap with all of those other people. We have cleaning people that support the office building, mowers that mow the lawn, cafeteria workers, the guy that runs the on site gym, the marketing people to sell our product.
And this is for a boring every day product that you wouldn't think twice about. That single device in a single niche industry pays the salary of easily 1000+ people. Multiply that by every little thing out there and it adds up quick. So no, there aren't a TON of a single profession out there but the workforce is made up of a ton of little professions that add up.
That extends to the modern trades as well. I have friends that are plumbers and electricians. 90 years ago there may have been one type but you have people that specialize in residential vs industrial vs medical.