The evidence is that it is a hard problem that is not solved. No amount of people who can't do the task demonstrate the existence of experts who can. Google and Microsoft have shown us examples of failing at simple HR tasks for years or decades with budgets for HR that dwarf a small companies entire payroll.

What virtually every attempt shows is that it is better to hire people who are roughly qualified and see what happens, managing the results instead of filtering. Having an HR strategy for hiring leads to creating biases (i.e. requirements based on your current work force) that gets you a group of overly similar and therefore collectively incompetent work force.