The existential condition that applies to both men and women isn't a cultural construct, so that's a basis for egalitarian ideals on humanist grounds.

Ken certainly has an existential crisis in the movie, and I'd even say the movie focuses more on that than Barbie's. But Ken's crisis is essentially to learn to accept feminism, not the upshot of evolutionary psychology. Ken is threatened by his role as Barbie's sidekick (as designed by Mattel).