In other words, billionaires/oligarchs have sequestered so much cash that it has outrun investment opportunities. What does that tell you about the theory that tax reduction spurs investment?
Helicopter money which deletes loans (meaning it would not punish people who did not borrow) would be a far better strategy in this case, and lead to both inflation and deleveraging at the same time, something which is impossible with other methods.
Also the whole tax reduction statement is mostly an opinion. From what I've seen, most companies are almost purely motivated by the risk-adjusted post-tax profit that can be obtained from the investment. Every idea on the drawing board is effectively evaluated meticulously on this basis. If that number isn't to their liking then the research/project simply never gets funded. The company might opt to simply do share buybacks or pay a higher than normal dividend. Plus the overall argument is mostly junk because the United States heavily reduces taxes for companies that perform R&D through the R&D tax credit.