Psychometric testing is a product invented by psychologists, mainly to justify their existance and created a need for, u guessed it, psycholgists. Some will even admit it.
I recall reading a study by the US military, I think it waas the US Marines, the did a study where they used the best psychometric screening tools to select 50 perfect candidates and trained them in a task. They also selected another group of 50 candidates, at random and applied the same training to them.
The end result was that there was almost no difference in the outcome. Both groups performed to the same standard in the required task.
It boils down to psychologists wanting to quantify the un-quantifyable. A human cant be broken down into a series of stats and numberss.