I don't think that was implied.

That immigrant founders tend to be amazing people statistically makes a lot of sense. The US government doesn't just hand out visas. They go to highly educated, successful people. So when comparing the highest achievers from another country with the average achievers from our own country, of course immigrants look good. Comparing our highest achievers with highest achievers from abroad would yield a more even comparison.

There are of course also seasonal worker visas and such, but those immigrants are not the ones founding companies (nor stealing jobs unless you want to break your back in a field all day).