I should have said, do these jobs more efficiently. Maybe I'm naive, but I don't see how a machine that does a "sizable portion" of the work would ever be good enough to be worth using. A human expert would always be needed to check the work.

If the proposition is that this would lead to fewer humans being needed for these jobs, I suppose that could be the case. In my own field, my criticism of automating, say, legal research and writing, is that the time it would take for me to check the work would be nearly the same as doing it myself. I don't see much efficiency gain, which is why I think the only thing that would truly be better than a human would be an AGI.