I am firmly convinced that whoever believes this suffers from a fatal misconception.
Although it has clear political implications, the last part of the quote-within-a-quote ("They are not our equals…") is a scientific hypothesis. Does it strike you that people who take the opposite view of Einstein's—or who even consider its possibility—are treated as merely mistaken? As suffering from a misconception? No—they are treated with opprobrium, condemned with epithets (racist, fascist, etc.), and purged from civil society.
No reasonable person denies that the ancestors of slaves were mistreated, but as an explanation for group differences this is not mutually exclusive with cultural or biological factors that may have nothing to do with past oppression. Unfortunately, this subject is not treated as a scientific matter—it has become a political fight. Einstein appears to be "ahead of his time" not because of the triumph of his scientific arguments but because his political allies have been consistently advancing.