Let's tell Singapore, a high-trust country with exceptional quality of life and extremely strict, borderline eugenic immigration policies, I'm certain they're missing out!
However, pointing to a different country that achieved success with “eugenic” immigration (it’s not even clear what you mean given that Singapore has had very high immigration but for the sake of argument let’s assume it’s the opposite of whatever the study here found) does not invalidate or disprove that the U.S. deficit reduced due to U.S. immigration.
It’s the kind of logical fallacy one would hope a 4 year old would grow out of, and yet…
I don't know how you get "eugenic" out of the Singaporean nationality law, full stop. Income or skill is not genetically bound, after all. The US, in fact, does have explicitly eugenics-based criteria in its naturalization process in that it retains the quota that existed in some form since 1882 but simply added a step in front so that it can claim to have removed to quota from where it was while maintaining a de facto quota system that only affects four nations - one it once colonized, two it has a history of vilifying in overt racist terms. In addition, even though USCIS employees are not doctors and are not trained in diagnosing or determining mental illness and its potential impacts or lack thereof, one is frequently asked at the citizenship interview if one had been diagnosed with a mental illness, and since stating an untruthful answer is grounds for removal and also a minor but extremely easy to prove felony, even erroneous diagnoses or conditions that pose no danger like ADHD may result in rejection of otherwise eligible applications. Since there's no "cure" for many of these conditions it puts the applicant in a sort of limbo, and this is asked after background checks and a ridiculously thorough vetting process that essentially had been going on for 8-10 years had been passed. On that front, I think America has Singapore beat.