> Brain draining the rest of the world is one of the main reasons for America’s success.

Not true. America was successful regardless of immigration. For example, for much of the 20th century, the US banned immigration from most of the world. Look up the history of US immigration bans. It's quite enlightening

> It is due to America being a nation of immigrants that we can do this.

America is not and never has been a nation of immigrants. At no time in US history has immigrants represented anywhere close to the majority of the US population. America was always a nation of native born americans. Not immigrants.