Productivity = Doing more things Efficiency = Doing the right things

I wrote a whole thesis on the subject AMA

Even Linus is conflating “doing more” with “being more productive”.

No he isn't:

Torvalds’ broader argument is that generating code has become easy, while maintaining a system over years or decades remains hard — and AI does not close that gap on its own. Without a working understanding of the underlying architecture, he suggested, AI assistance can help someone make mistakes faster rather than build something durable.

I understand what you're trying to say, and even agree with it, but the car factory example is just wrong. Those have a design speed that is generally limited by cycle times for individual steps. Like a robot has to place say 10 spot welds. You can't speed that up. To stick with this example: in theory you could add a robot so both place 5 spots, but that rework takes probably a year and costs millions. Plus you don't have one bottleneck like this, but a lot of them with similar speed (hence the "design speed" of the whole factory).

You can slow the whole factory down to run under capacity (or not run it during night shift), and then you have room to speed it up. But if you're running at capacity, there is very little you can do.

It's physically impossible to speed up the factory to 1.5x, let alone 10x.