All the research I've seen shows that people are lousy at these.
I don't doubt that most people suck at it. One of the four people who co-founded YC is hardly "most people." Your general skepticism fails to be a good argument in this specific instance.
How about this: I'm skeptical of YC and PG; I think much of the touted philosophies lead to success "in spite of" instead of "because of", and I think people naturally want to feel superior which in the case of this community means special insight or cold hard truths, when really most of the time it's just pretty pedestrian ways of operating that are echoed in thousands of companies. The concept of the guru is ancient; this is the latest iteration.
I don't doubt that most people suck at it. One of the four people who co-founded YC is hardly "most people." Your general skepticism fails to be a good argument in this specific instance.