As you can see, the evidence does not support your post at all. America was 84% white people in 1930. The primary minority was black people. Other groups were negligible.
That’s not a very diverse racial mix. It stayed that way for decades after that.
To be totally frank, if you actually try to measure whole populations for “superiority*”, Asians usually come out on top. I’m hardly a white supremacist. (and if you must know, I am not asian myself) All I’ve been saying is :
a. The facts are, our ancestors didn’t in reality let just anyone in pre-1920. I don’t know where the 12 million Chinese workers went, they aren’t there in the census data.
b. Some people are probably better than others as individuals, regardless of race. We should go by merit instead of having just “no limits, anyone and everyone”. Also if our merit system happens to favor people who happen to be from some races more than others, we should still use it, so long as the system is in fact race blind. There is an argument for affirmative action to make up for past wrongs towards our own citizens, but I do not think this should apply to immigration policy.
*metrics like crime rate, higher education completion, how hard someone works, intelligence, child geniuses, it’s mostly asians winning the competition by large margins.