If you have objective criteria, there is probably no bias. But I would still consider what they say, because it might exist a bias you haven't noticed.

I mean, we all have bias that we haven't noticed.

In a project, I was passed over on a promotion that went to a friend of my (male) manager. The problem was that just after giving him the promotion, that manager asked me to teach him how to do the work, because he liked the way I was doing the job for that position.

So I naively asked why did he gave the promotion to someone who didn't know how to do the job when I already was doing it well. His answer was that "He had lot of potential". the implication was that I didn't have potential (go figure). So I asked for a change of project and the manager was livid, because why would I want a change of project if they were so happy with my work? Point is, that manager also had several women in the team a probably thought he didn't had a bias. In his mind, he wasn't being unfair to me, since "women are less ambitious" and he telling me he was happy with my job should have been enough validation. You see, "he valued my job", just wasn't willing to give me the promotion for the job I was already performing well. He, instead, was willing to offer me "security". Because of course he wanted me to stay in the team and keep doing the job.

Now, maybe it was "feminism" telling me that it was unfair. On the other hand, by changing project, I ended getting the promotion that manager denied me. If I had stayed, I would have never got it. So maybe feminism wasn't offering that bad advice. Meanwhile, after I left, they did have productivity problems in that project which I doubt there were just about me, but about that manager driving away talent. The manager wasn't fired, by the way. Not his friend who didn't know how to do the job. They were allowed to perform below par performance and moved to other projects when the customer was lost.

You can make your own conclusions or think that I lie. But this show how manager can create opportunities for some, while denying opportunities to others. And it happens all the time.