I thought the claim was that there is not true upward mobility. Are you saying that immigrant’s are not encountering “true” upward mobility? What constitutes “true” upward mobility?
The fact of the matter is that newcomers to this country with little to no wealth, who frequently barely speak the language, and low earning power still produce children that jump ses classes every generation for the first generation or two.
Could it be better, sure. We should absolutely get rid of things like legacy preferences and increase the estate tax.