OK, sure, tax wealth of the rich -- if you can somehow outdo their self-interested political action. Even the most extreme viable wealth taxes proposals target ~2%.

My question is really the economic efficiency of their other 98%, which is becoming about half of available resources.

I suspect the evidence would show their investment gains are less from productivity and more from coordinated extractions, and that there are severe limitations that come from consolidated decision-making (after all, the premise behind the market is that the collective is smarter than the king). Not to mention that buckets of money probably are also alienating and defeat healthy self-discipline, particularly for the next generation.

I would love instead to find that new money seeks and creates new opportunities, particularly those that are beyond what you can convince collectives to do.

It's pretty obvious that ants threatening elephants won't go far, but (to abuse the analogy) I suspect elephants would take helpful hints. Expanding wealth inequality should make it easier for great ideas to take off, so perhaps that's a better focus.