It also relies on blank slate theory - ie that all groups should perform equally, and if they don't, that's evidence enough that there is a conspiracy against them.
Perhaps a way to test the "different groups have different abilities" vs "past bias" theory, would be to find people with high IQ / historical record of accomplishment who suffered great historical discrimination and deprivation (eg Ashkenazi Jews from the holocaust, Chinese families purged in the great leap forward) and then compare their descendants test scores and job outcomes in the USA.
You could look at outcomes a generation or two afterwards and tell whether their performance was high/low ie was "reversion to high group accomplishment" or "underperformed due to present or previous oppression"
Perhaps a way to test the "different groups have different abilities" vs "past bias" theory, would be to find people with high IQ / historical record of accomplishment who suffered great historical discrimination and deprivation (eg Ashkenazi Jews from the holocaust, Chinese families purged in the great leap forward) and then compare their descendants test scores and job outcomes in the USA.
You could look at outcomes a generation or two afterwards and tell whether their performance was high/low ie was "reversion to high group accomplishment" or "underperformed due to present or previous oppression"