Send, I suspect DS can live with not getting through the first filter. The previous year he passed the final, assessment stage, for an internship with the same organisation (though was not offered a place) so it was odd. Presumably the first sift this year was seeking a different balance between technical skills and other attributes, including diversity. He would have scored highly on the first, but not the second.
And thats really the point. Selection means selection. Some people get places, others dont. Previously interviewers may have used criteria they personally thought were important. Including perhaps the University you went to as well as a golf handicap or gender. Now an organisation may decide the criteria they are looking for in advance inter alia to avoid indiviual prejudices. Whether they get these right, or whether the tests accurately measure applicants ability to deliver to these criteria, is anyone's guess. There will still be a limited number of jobs and so some will get them, others wont.
The medicine threads will throw up examples of weird Situation Judgement results. And individual recruiters will claim that the pre-screening means candidates can be rather samey. But from an individual's perspective I suspect if you are well qualified it will still be a case that you get some jobs you apply to, but not others.
The losers may be those who have generalist degrees from 'good' universities, who assumed that they could always apply for accountancy or the civil service. The jobs are still there, but without a rounded CV offering skills and experience beyond a degree, you might struggle. The competition is strong and recruiters will be looking beyond the degree.
From observation there are certainly a few recent graduates, even from Oxbridge, who have been surprised at how tough the graduate job market is and who have struggled.