A thoughtful question. The trouble with unique and precious individuals is that if they have nothing in common, then we cannot apply previous knowledge to help them. This would apply equally to, say, kidney disease or dyslexia.
My heroes in psychiatry were the clinicians who spent years talking to the inmates in asylums, trying to discern commonalities and patterns to mental illness, against a prevailing belief that people went mad in their own individual ways. Charcot, Breuer, Kraeplin and Freud, and the many others who laid the foundations for a more methodical approach to the understanding of mental illness.
To reassure you : our next phase in the research is to take what we have learned from the quantitative work (which was based in turn on focus group interviews) and conduct more qualitative research with students to try to understand the phenomena that we have uncovered. It’s an iterative process.
But it’s based on the idea that people have sufficient in common to be understood, in part, by generalisations. If they hadn’t, music would’t work, or anything that harnesses our common humanity.