I don't know if that's true. But it makes sense that people earning more than $10M don't show it in the W2.
That's why we should be carefull with excessive taxes for bussiness - if some companies go bankrupt, or lay off 20% of their workforce as a result it might be a net loss to society.
And before you start arguing that sometimes companies make money on shady things: yes, they do, but then you don't punish them for that with taxes, there are criminal laws for such things.
None of this is illegal, but it's hard to argue a benefit to society in general.
Personally, I don't think it's right to have more than 50% tax rate at any level, and beyond say $50k/year would say that a 20-30% tax all the way up without deductions would be better. Eliminate corporate taxes, limit corporate capital holdings requiring either reinvestment or divestment to shareholders (who are then taxed).
Simplifying and automating the system better would work better for everyone involved. But confusion keeps Intuit/H&R Block and others in business.
It's a fallacy verging on propaganda to argue that a reform should not be pursued because another policy can be used as a loophole. All that means is that the reform needs to be more holistic to be successful.