No one ever said that screening measure might not have false negatives. The only way to guarantee that no desirable immigrant is ever turned away is to never turn anyone away ever, since there's always a chance. This is not to say that immigration could not be reduced drastically with minimal effect on startup cofounders, based on the research in OP which is being cited for drastically different claims than it implies.
> I also see that you are listing a lot of countries with very small populations and an even smaller number of legal immigrants.
In my sarcastic aside, I listed countries by order of the WP entry; they may be small countries, but they have nevertheless managed to send an awful lot of people into the USA. Numbers is not their problem. And if you are referring to the list of startup founders, many of them coming from small countries (with even smaller immigration into the USA) only emphasizes the disparity in odds between countries...
I also see that you are listing a lot of countries with very small populations and an even smaller number of legal immigrants. If they don't show up in start ups, that would be the first thing I'd check. Not their supposedly lower IQ or education, which I would reject in the case of some of these countries.