Nah, western developed nations certainly have a disproportionate amount of unhappy people. It's because we lack responsibility and thus, meaning in our lives.
Discussion
You underestimate how shitty human existence used to be and how many died young.
And that isn't even accounting for the wars, with their mind-boggling casualty numbers.
No I know how shitty human existence was, and not that long ago. But they had a reason to keep going. People forget, the wild West was only a couple hundred years ago. We were savages. Life expectancy and suffering don't equate to happiness. I suppose when I say happiness, I really mean "meaning"
People would be a lot happier today if they had more kids. Again, people in undeveloped nations, with low life expectancy, very very hard existences, are happier than a lot of westerners that have nice cushy lives.
They actually have a weird, temporary advantage over us, as they have many of the things that actually improved our well-being (canalisation and sanitation, basic medical care, adequate food supplies, electricity, widespread literacy and understanding of fertility, etc.) without as much of what the Germans call Wohlstandsverwahrlosung.