I think it's one of many factors we should look at.
If I am looking at two applicant for rad onc residency, who went to the exact same school, same GPA, Step scores, amount of research, extracurriculars, both had college-educated, middle-class parents, but one was white and one was black, I would choose the black applicant. Undoubtedly, the black applicant faced more obstacles to get to the same place due to racism, be it systemic, overt or even just microaggressions. Racism definitely exists and it could have been a particular teacher/professor/teaching assistant they encountered along the way that made it more difficult to obtain the same grades. Middle-class white parents will have more connections than middle-class black parents, which could amount to less shadowing opportunities, less research opportunities or not getting a stellar letter of recommendation from your white family friend who is the dean of some school. These many little things matter.