The goal of interviews and assignments is not to achieve an outcome but to assess someone’s abilities. Henceforth, cheating cannot be justified.
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.
Maybe to the interviewer. But for the applicant the goal is to achieve an outcome.
I can assess his abilities either way.
In short, the interview process worked as intended.