The rest of your post seems to be talking about cases where the market changes and the labor force changes as a result. But we're looking at the opposite, right

The rest of your post seems to be talking about cases where the market changes and the labor force changes as a result. But we're looking at the opposite, right? We're looking at a direct change to the labor force, and there may or may not be any commensurate change in the market. So I don't see how your example of the transition from agrarian society applies, at least not directly. By the way, I'm asking these questions in earnest -- this isn't a debate to me, and I'm more than happy to "lose". I don't know much about this topic and would like to learn.