If "pursuing happiness" is an incentive for modern societies, pursuing something else - improving oneself I suppose - would become an incentive when most of population have achieved "happiness" (and misery should present itself to the world with a brave new meaning?). To my perception, that is, tsuyoku implies "always pursuing" while happiness achievement implies an end of the line.

...we need other people below us to be happy

Interesting connotation. "Below us" implies we' re already there, and by some sense of altruism we desire unhappy people to be happy? Or is it a different classification?