I haven't yet read this recently posted article, but I plan to, as it seems to be important (and is by good researchers). But here is the key finding from its abstract:
"Using administrative data linking 10 million firms to their owners, this paper shows that private business owners who actively manage their firms are key for top-income inequality. Private business income accounts for most of the rise of top incomes since 2000 and the majority of top-earners receive private business income - most of which accrues to active owner-managers of mid-market firms in relatively skill-intensive and unconcentrated industries."
This would appear to suggest that the proposed lower tax rates for business owners of pass-throughs are almost precisely targeted to increase high-end inequality as much as possible, in exchange for as little efficiency payoff as possible. These probably tend to be people with low labor supply elasticity and/or who are in effect reaping rents.