To be honest, I'm not sure if you're proposing me questions or are expecting me to propose questions to you. The bottom line is the US economy as it exists today has moved beyond the specialization presented in your video. I can understand that we could disagree as to why, but at this point I'm not sure you even agree that we've moved beyond that, and should be questioning why. Do you really think our economy is still in the process of specializing?
Oh, it's definitely becoming more specialized in the sense that the video meant. I didn't think that question was as interesting as the Wall St.-versus-managers dynamic, so I didn't comment on it. But I definitely thing it's true.
Look at Footballguys. It used to be the the writers were all-purpose fantasy football writers. Now some people specialize just in IDP leagues, other specialize in dynasty, others in Daily Games, others in injuries, and so on.
It doesn't matter that Footballguys as a whole is still a diversified generalist. What matters is that the individual writers are more specialized: that's where the efficiency gains come from.
It's the same in other industries. There used to be biologists; now there are geneticists, protistologist, biochemical engineers, biogeographists, etc. Same with medicine, law, software design, and so on. People are specializing more and more.