I think being smart universally trumps being less smart - but the definition of smart needs to be more encompassing. For example take the stereotype of a brilliant man or woman who neglected family for career, and are forever single and childless forever -- while someone less brilliant just "ends up" with a family and ultimately more fulfilled in life. Superficially this is an example of an average person being happi…
As a single and childless person, I don't like the implication that those are marks of a less fulfilling life. I know some people married with kids who seem very happy and fulfilled, and some profoundly miserable and trapped. I may be missing out on some good things, but I'm also avoiding some extreme misery, and generally do feel content and fulfilled.
Plus, kids who grow up with parents who are unhappy and would prefer to be childless are probably a lot more likely to grow up into unhappy adults.