There are only three possible outcomes from this tax reform.
The first is companies will have more retained profit.
The second is that they don’t invest it, but do share buy-backs instead.
And the third is that the wealthiest in the US will get wealthier at cost to everyone else as a result.
What happens then? What’s the next effect?
The wealthy either spend the money, increasing demand, or the wealthy invest the money, increasing both the productive capacity of the society and demand.
Sure, we can argue about how effective this is but to ignore it means you’re not doing economics.