Isn't this a situation where focus on the details loses sight of the big picture?
Would you argue nature/nurture is not a valid concept/dichotomy?
Yes, people are very complex and nearly impossible to place in any particular box, but that doesn't make their approach to the world completely arbitrary.
It seems like closely examining all the trees and declaring the forest doesn't exist, it's only just trees.
At 60, I've certainly people watched for enough years to sense more than enough character traits coming out in the people I know. Whether the sciences can find ways to measure them or not.