But can Bob actually do that with agents, without limit? Right now, he's going to hit a ceiling at some point, and the Alices of the world will run circles around him.

The question is: will agents improve to the point that even the most capable Alices will never be needed to solve problems? Maybe? Maybe not? I'm worried that they won't improve to that degree.

And even if they do, what is the purpose of humans in this world?

I think the real issue is that no, he can't, but corporate and government entities that decide won't care. Things will simply get worse. The problems will be left to fester as things that simply "can't be done".