I am focused on the topic and I cannot ignore the part about your wife’s K1 being approved by someone from the same ethnic/cultural background because that is the whole basis of your argument about prejudice and bias. She would’ve been approved even if the interviewer was white American who, let’s say for argument’s sake, was anti-immigration and had prejudice towards people from her country.
To answer your question, I’m sure there are some officers who have prejudice and bias but no, I don’t think it’s pervasive and widespread. In that case hardly anybody would get B2 visas. Per the Department of State, in 2022 alone, 1,244,484 B1/B2 visas were issued worldwide.