There is a very simple statistical answer to this, that blacks come to the US as labor force are of far larger quantity than asians, forced or not. Let's assume it to be 50x vs. 1x
But for the new immigrants, the percentage is in the same magnitude, as the US implemented quota-based immigration system for countries.
Let's say its 4x vs. 4x, and added together, it's 54x vs. 5x
Why do Asians Americans in general have better socio-economical status? Because the US simply doesn't allow new immigrants with low socio-economical status to become American citizens. And for those Asian Americans who's in the lower half and in much worse shape because their socio-economical status, their difficulties are destined to be worsened by affirmative action rather than alleviated.
Affirmative actions benefits the top percentiles of racial groups, rarely the lower percentiles. Let's say the affirmative action benefits the top ten percents. For African American, it's 5.4x which is more than the 4x who are new immigrants. For Asian American, it's 0.5x, which is less than one eighth who are new immigrants. New immigrants always come from better half of the socio-economical status.
That is, with affirmative action, if your ancestors are labour force came to the US forced or not, your life would be much harder as a Asian American than as a African American. Because as an Asian American, you are competing mostly with new immigrants who are top talents/money. And fortunately as African Americans, you are competing with people with largely similar socio-economical status.