It's a fair point that income inequality has been driven to great extent by the professional class. But the message behind the article is that everything's fine because labor's share of income has remained stable. The problem is the growing inequality, not the identity of the people taking a disproportionate share of the income pie.

Tax-and-transfer is a response to inequality, and so necessarily lags the problem it tries to address. If current policies were truly maintaining the status quo from 50 years ago, then it follows that wealth inequality would be increasing linearly, and not accelerating as it is.