One thing to consider is the fact that America during the period 1992 to 2020, has seen a vast societal shift from nerds being seen as social outcasts to being seen as the thing a huge portion of the people at the top of society claim to be.
As a counterpoint, I wonder if the exact same study, when conducted in an anti-intellectual society (say Nazi Germany in the late 1930’s) would still return the same results, or if the people that were “held back” would end up better off psychologically.
I strongly suspect the huge change in how cool it is to be nerdy today is a significant factor in today’s wellbeing.