If you take the population of black Americans you’ll find that the overwhelming majority of them have their history in the ~3.9 million people trafficked during the slave trade and the following diaspora from the south throughout the 40s-60s, the majority as in 80%+. If you look at Asian Americans, you’ll find that the overwhelming majority of them do not descend from the ~20k transcontinental railroad laborers.
It’s not hard to tell that their experiences must be vastly different, because 20k is a very small proportion of the total Asian American population, while 3.5m is a much larger percentage.
I hope this help you with differentiating how relatively homogeneous groups are.