The truth is for me somewhere in the middle. Happiness and satisfaction are not absolute, they can exist only in relation to your surroundings. Thus younger people in the US might be objectively better off than people in say India, but that doesn't matter. Their surroundings are as the OP described and that dictates how they feel about the present and future day.
On physical health it's actually wrong for the US as people's physical health is deteriorating evident by the falling life expectancy.
But with all that said, the actual idea in Japan is for me pretty stupid, as I consider dating apps to be one of the reasons people are connecting less and less. The choice is too large, it's very superficial, most people want the "best" thus large number of people are out of luck.