the general average across humanity.

Aren't you making the assumption that the average applies to everyone? It does not. There is a rather wide spread and pretending that a single average value represents it well enough is unwarranted.

There are certainly things biologically hardwired into human brains but not all of them are terminal values and for things that are (e.g. survival) you don't need a neurobiologist to point that out. Frankly, I am at loss to see what neurobiologists can say about terminal values. It's like asking Intel chip engineers about what a piece of software really does.

how little the average person knows about what they would actually happy with

I don't know about that. Do you have evidence? If a person's ideas about her happiness diverge from the average ones, I would by default assume that she's different from the average, not that she is wrong.