An implication of Wilkinson’s theory is that intergenerational mobility should decrease over time. Wilkinson claims intergenerational mobility has decreased. It hasn’t (estimates from Lee and Salon 2009):
The “intergenerational elasticity” (the percentage kids’ incomes raise for every percentage increase in parents’ income) has stayed about the same over the last couple of decades. Other studies get contradictory answers and few find a statistically significant trend.
Which suggests the answer to the question posed in the title is: none of the above.
UPDATE: On rewatching, I see that Wilkenson isn’t trying to explain increasing inequality as I first thought, he’s trying to explain non-existent decreases in mobility.