It's not about the feasibility of the technology.

If "human brains become fully irrelevant economically" then that brings into question the entire premise of "share holders" and "financial winners".

What even are money, shares, stocks, and finance in a world where human brains are irrelevant economically? No one knows, but betting that "share holders" will be the winners is a highly questionable bet.

I would much more likely bet that "the armed group who manages to control and benefit from the AI through force" will be the "financial winners" more so than "share holders", who tend to not be terribly military minded at least in America.

LLMs are not emulating the human brain. Somebody may well be able to do that someday, but right now nobody is even trying to.