> An average software dev today is expected to do the work and have the skillset that used to take a half dozen people or more.
I think that depended (and still depends) a lot on the organization and the nature of the product.
I distinctly remember doing backend and some frontend development, requirements specification, database design, customer interfacing and even a bit of ops, all on the same job and with the same title in the 00's. That was in a small-to-medium company and my clients were on the small side so the projects might not have even had half a dozen people to begin with.
Larger organizations and more enterprisey projects would have had more specialized and limited roles: customer/specs people, possibly frontend and backend devs, DBAs, testing people, and those in charge of ops and environments. In my experience, that's still more or less true in enterprisey development today.
I think a part of the problem is that while new technologies have emerged and reduced the need to manually work with some older or underlying technologies, they haven't replaced previous skills.
Containers have reduced the amount of work needed to deal with deployments and environments but they haven't removed the need to know servers or operating systems. Cluster management can reduce the amount of manual work on setting up containers but it doesn't remove the need to know the underlying container engine. So now you need to know Linux servers and containers and k8s and whatnot just in order to manage a local backend development setup. At the same time, frameworks have made a lot of frontend work more manageable but they haven't made JavaScript or other underlying stuff disappear.
Thus the scope of what being a fully-versed full-stack developer entails has grown.