Doesn't this assume that what humans are current doing with LLM agents is working out? Isn't it a bit early to bet on that to this degree?

Not when all of the marketing of LLMs is touting their abilities to do the exact thing and that is what investors are being presented.

If it is as you say, then eventually the house of cards will crumble. Then we can finally go back to work and quit being inundated with needing to use AI for everything.