Inequality vs. the productivity slowdown

Greg Mankiw writes:

The Economic Report of the President was released today.  A friend draws my attention to Table 1-3 on page 34, which presents several historical counterfactuals.  It finds:

1. If productivity growth had not slowed after 1973, the median household would have $30,000 of additional income today.

2. If income inequality had not increased after 1973, the median household would have $9,000 of additional income today.

So, which is the bigger problem?