you're still employing only one man for every hundred people worth of productivity
You're still making two mistakes. One assuming that every robot is used to kill already existing jobs, and two assuming that for every job lost two more cannot be created. I've already argued to second point in several other posts, but I'd like to try and convince you on the first point where I believe you are mistaken. In this post I argue several points where robots can create a net gain in jobs, some of which cause the loss of no jobs at all. The problem you and others are stuck on is arguing about current robots while supposing a future robot. To this point, all robots have ever done is displace factory workers through automation. This is because they are uniquely suited for this type and work and really nothing else.
But robots of the future will be suited for much more, to the extent that they 1) augment human abilities and 2) extend to endeavors otherwise inaccessible to humans. In these scenarios, you aren't replacing anybody, or maybe a few people, while enabling work for dozens, hundreds, or even thousands by creating jobs were none previously were able to exist. If we're talking about robots of the future, you have to give them more capabilities than just those that replace menial labor.
And it's worse than that, because unlike humans robots lend themselves to modularity - there's no sense in maintaining a vision-systems repair specialist if you can simply unplug the faulty system and replace it with a new one more cheaply.
Again, you are assuming a robot of today for a robot of the future. Robots *today* lend themselves to modularity. Robots of the future? Already we see emergent behavior we can't fully comprehend when a whole system is working together as a whole. For instance (I don't like to go down the sci-fi very distant future path, but since everyone here likes to argue about machines with extreme intelligence replacing humans I'll do so for the moment), consider a robot brain with billions of interacting neurons. Perhaps it's not possible to download and replicate such a thing. Consider robot with some proportion of biological parts. Perhaps such a thing is not easy to repair. I don't know that's just a little sci-fi there.
Back to reality and with respect to vision in particular, we employ many computer vision experts. Robot vision gone wrong isn't just about the camera. When robots are seeing the wrong thing, sure you can replace their vision systems, swap in a new one, but then when it's still seeing the wrong thing, what do you do? It takes a specialist to figure it out. This is the difference between a robot repair man and a TV repair man; one is dealing with a single-purpose solid state device, while the other is dealing with a highly nonlinear system which is interacting with its environment and making decisions on its own. One of the two is exponentially more complex to service.
You only need a human involved for non-obvious problems, which probably means someone who is reasonably well versed in *all* the component systems of at least a specific class of robot
And you expect such a person to exist? Already in robotics we have dozens of specializations.
Not something Joe Sixpack can reasonably be expected to learn to do.
That's why Joe Sixpack doesn't become a surgeon when he's displace from his job, he trains to be a nurse or an orderly, or a sales rep.
And as for the technician support staff - how many do you really need?
How many does a hospital need? There are many more nurses than there are doctors and surgeons.
just look at what's happened with customer service in the last decades, it used to be you talked to actual humans on the phone, now you've got to go through several layers of poorly-automated systems designed to handle all the common situations before you'll even be connected to a human.
This is a perfect example of why human-facing automation is still very far off. The push was toward automation in call centers because it saved money. But the result was/is so bad that it pissed off customers. Now live people behind the phone are used as a competitive edge. Most any human-facing jobs out there are safe for a long long time to come; humans are fickle and nuanced, and it takes another human with skills like creative thinking, deduction, inference, and (the biggest one) true empathy in order to meet the needs of another human. Robots may try to (poorly) take these jobs away, but the pendulum will swing the other way when people get fed up dealing with the incompetent robots and humans will again be employed.