Of course you’re right that children of US Asian immigrants are ahead even of US whites, I mention this in my different comment in this thread. However, since there are few of them relative to other groups, they don’t affect the distribution much, so I didn’t mention this for the sake of clarity, as it didn’t detract from my main point.

There are not few of them relative to other groups. In fact there are more of them than several, more native groups, like Pacific Islanders, Native Americans, and Mixed Race people

Well no, East and South Asian immigrants to the United States do tend to outperform the median in their country of origin. Acutely, in the case of South Asians.

So that's half of the statement, the other half is that those two groups are not a large fraction of the total immigrant population. As such, they affect the conclusion, in the sense that removing them from consideration would make the difference in question starker, but they do not change it, because it's a statement about a whole of which they are but a part.

We don't exist because it's politically inconvenient to remember.