I think your concerns are totally valid and important to the design community.

I personally try my best to avoid those biases while doing interview but as we all know, it's inevitable. I wish that all interviewers know that they have the responsibility not only to find the best candidates but also to give the same opportunity to all designers, and to have wisdom in their judgements.

What I think is the most practical solution to this issue is:

1. to always have more than 3- 4 different people handling the interview process to avoid subjectivity

2. to have separate feedback review form so all opinions won't be influenced by the others

3. to have clear role specification before the hiring process so we know exactly what kind of metrics that we should be looking for. (just like what you said, we cannot generalized all kinds of designers into one product designer requirements)

4. to be as humane as possible and think about the ethics, equality, and always open your door to rejected candidates if they want to try again in the future.