Wrt your points about wealth holding and investment, you're assuming the allocation of a billionaire's wealth is efficient and productive. This ignores that private returns are not social returns, it assumes that growing capital is what is best for society, and frames the question as investment vs consumption, when the question is "who controls investment decisions?" Your argument smells very similar to Reagan's trickle-down economics which has been disproved through decades of data showing tax cuts don't generate promised growth. Inequality continues to increase, while median wages stagnate.
I agree invested capital finances production, but I disagree that extreme concentration optimizes for this. Broad and diverse investment mechanisms would allocate capital more effectively than a small number of individuals basing their decisions on private returns.
Consider the equation of exchange: MV=PQ (money supply x velocity of money = nominal GDP). As wealth concentrates, velocity in the real economy decreases. Billionaire capital cycles through financial assets instead of cycling through the real economy (wages buy goods and services which pay wages). A lower velocity means either lower GDP or central banks must increase the money supply, risking asset bubbles (hmm, sounds likes whats happening right now ). Evidence suggests a dollar is stronger in the hands of the working class creating immediate economic activity and supporting local businesses, compared to a dollar in an asset portfolio.