[quadrangle]

How about equity instead of equality?

Anyway, "social mobility" generally just means there's no caste system or effective caste system. If the inequity in the system means that a small percent of people hold most of the wealth and power, what difference does it make if anyone has a chance to join that elite?

In a zero-sum game, social mobility is better to exist than not but it isn't going to actually change anything fundamental.