I also think sometimes people who come from privileged groups (white men, of course, but even persons with specific university backgrounds) may feel more comfortable citing mentoring experiences and operating well on a team (and been given the opportunity to mentor earlier on), since they feel they are already assumed to be qualified, while someone from a less privileged background may feel even unconsciously a desire to demonstrate their worth by citing their personal accomplishments, versus citing how they worked well with others.
I think that is very true about the onboarding and supervisory process–many organizations are so convinced that “if you hire the right people, everything will go well,” which is only true to a point–they focus a great deal on the hiring process with HR, but on retention and training, not so much. This also circles back to using more contract workers nowadays. I see more and more companies just wanting to hire a contractor temporarily who knows X, versus hiring an individual as a permanent employee.