If the assessment has no relationship to the job requirements then the test assessment cannot be justified either
1. They are considered high performers (maybe promotions are on a schedule?)
2. They are actually high performers (some people can bullshit their way through a job for years).
3. They are outperforming a hypothetical person who didn't cheat on the test and would have been hired instead of them with an honest assessment.
The justification foe the assessment is that the assessment is the defined set of hoops that the company who you are trying to get paid by has assigned.