The fault is that your argument builds a straw man that the wealthy do *no* good by holding/using wealth, but that isn't the argument. The argument is that they do relatively little with that wealth. One two million dollar car churns the economy, as in, provides jobs, taxes through fees, etc, much less than one hundred 20 thousand dollar cars.
A similar thing could be said of a house. A 70 million dollar house doesn't generate 100x the economic activity of 100x 700k dollar houses.
Partly this is because many "premium" materials don't generate more economic activity than less premium materials at a fraction of the cost...but the increase in cost is due to rarity and desirability only. Another part is that high priced items tend to require a one team work longer rather than more teams work, concentrating the transfer of wealth rather than spreading it out over broad actors who can trickle wealth down much faster and efficiently than a few who have a large share of it.
The idea of "trickle down" is valid, it does happen, but it is more like accidentally watering some plants from a leak in water tank rather than watering a field with irrigation.
And when your goal is to grow a crop like an economy, relying on minimal rainfall and tank leaks just isn't a productive way to go about it, as our Norse neighbors have shown.