this type of thing totally dismisses the whole gestalt of becoming who you are, and plops your whole existence and character on one trait.

I agree--and what a misleading thing this can turn out to be, as you discovered. I really wonder how accurate these
"predictions" would prove if they were applied to people who had lived in some kind of desperate situation their whole lives? We can't be all nature or all nurture, let alone happenstance. As you say, we are a sum greater than all of our parts.